| Nuewood Construction | Gary Lynn Adams | — | (805) 523 1636 | GC, remodel, ADU | Simi Valley · Ventura County | — | — |
| Numero Uno Plumbing | Numero Uno Plumbing | — | (805) 890 5254 | Other | Oxnard · Ventura County | — | — |
| Nunneley Construction INC | Nunneley Brian | — | (310) 488 1153 | GC, remodel, ADU | Thousand Oaks · Ventura County | — | — |
| Nuview Landscape Construction INC | Richard Sr Caldera | — | (805) 609 1070 | Windows, patio, painters | Simi Valley · Ventura County | — | — |
| Nyberg's Second Nature Landscape INC | Nicholas Ryan Nyberg | — | (805) 522 2226 | Windows, patio, painters | Simi Valley · Ventura County | — | — |
| O G Construction | Oscar Meza Garcia | — | (805) 797 8253 | GC, remodel, ADU | Oxnard · Ventura County | — | — |
| O'brien Woodworks | O'brien Woodworks | — | (805) 208 5996 | Other | Thousand Oaks · Ventura County | — | — |
| O'bryant Electric INC | Denise O'bryant Stayrook | info@obryantelectric.com | (818) 407 1986 | Electricians | Simi Valley · Ventura County | — | — |
| O'connor Electric INC | John Kenneth O'connor | oconnorelectric@comcast.net | (805) 376 6033 | Electricians | Newbury Park · Ventura County | — | — |
| O'donnell Construction | Charles Joseph O'donnell | — | (805) 216 0954 | GC, remodel, ADU | Camarillo · Ventura County | — | — |
| O'hara Construction Co | Richard Joseph Ii O'hara | — | (805) 889 4954 | GC, remodel, ADU | Port Hueneme · Ventura County | — | — |
| O'kane Construction | Patrick Gerard O'kane | — | (805) 216 6243 | GC, remodel, ADU | Ventura · Ventura County | — | — |
| O'neill Construction | Peter Gordon O'neill | oneillsusa5@aol.com | (415) 491-4091 | GC, remodel, ADU | Thousand Oaks · Ventura County | — | — |
| O'rileys Construction Co | Steven Shane Riley | — | (805) 428 3470 | GC, remodel, ADU | Simi Valley · Ventura County | — | — |
| Oak House Construction | Gilbert Gastelum Gonzalez | info@oakhouseconstruction.com | (805) 766 3406 | GC, remodel, ADU | Ventura · Ventura County | — | — |
| Oak Ridge Landworks INC | Kevin Michael Lydick | kevin@oakridgelandworks.com | (805) 630 8377 | Windows, patio, painters | Thousand Oaks · Ventura County | — | — |
| Oak View Construction INC | Humberto Mariano Vasquez Rivera | info@oakviewconstruction.com | (818) 699 5912 | GC, remodel, ADU | Westlake Village · Ventura County | — | — |
| Oaks Security INC | Timothy Craig Mc Carthy | — | (805) 499 1500 | Alarm and generators | Thousand Oaks · Ventura County | — | — |
| Oaktree Builders INC | Jonathan Joseph Knight | — | (805) 218 9919 | GC, remodel, ADU | Ventura · Ventura County | — | — |
| Oaktree Property Management | Oaktree Property Management | info@oaktreeproperty.com | (805) 653-7711 | Property managers | Ventura · Ventura County | — | — |
| Oasis Pool Care | Oasis Pool Care | maxtaylor@sbcglobal.net | (805) 520 6064 | Pool | Simi Valley · Ventura County | — | — |
| Obsessive Compulsive Carpentry | Obsessive Compulsive Carpentry | — | (805) 405 3534 | Other | Moorpark · Ventura County | — | — |
| Oc Custom Design & Construction INC | Omar Isaias Lara | — | (805) 797 5811 | GC, remodel, ADU | Camarillo · Ventura County | — | — |
| Ocean Air H V A C | Scott Raymond Jones | — | (805) 815 5624 | HVAC | Ventura · Ventura County | — | — |
| Ocean Point Property Management | Ocean Point Property Management | info@oceanpointrealty.com | (805) 849-1700 | Property managers | Ventura · Ventura County | — | — |
| Ocean View Decks | Jerald Glen Huffman | — | (805) 600 1107 | GC, remodel, ADU | Oxnard · Ventura County | — | — |
| Ocean View Plumbing And Rooter | Ruben Lopez Landeros | — | (805) 485 5678 | Other | Oxnard · Ventura County | — | — |
| Oceanaire Plumbing INC | Joseph Owen Iv Kern | — | (310) 902 0264 | Other | Moorpark · Ventura County | — | — |
| Oceans Electric | Brett Nelson Kaufman | brett@oceanselectric.com | (310) 595 8209 | Electricians | Simi Valley · Ventura County | — | — |
| Octavio Leon | Octavio Leon | — | (805) 890 0504 | Windows, patio, painters | Oxnard · Ventura County | — | — |
| Octoberbabies INC DBA Blake Schwermer Showerpans | Jonathan Blake Schwermer | — | (805) 551 3494 | Other | Santa Paula · Ventura County | — | — |
| Off The Wall Floors INC | Michael Owen Dwyer | — | (818) 521 7584 | GC, remodel, ADU | Moorpark · Ventura County | — | — |
| Og Plumbing | Og Plumbing | — | (805) 248 3275 | Other | Oxnard · Ventura County | — | — |
| Oglesby Construction & Design | David Brian Oglesby | — | (805) 444 5037 | GC, remodel, ADU | Ventura · Ventura County | — | — |
| Ohms Electric | Ruben D Chavez | info@ohms-electric.com | (805) 636 2774 | Electricians | Ventura · Ventura County | — | — |
| Oilfield Electric Company LLC | Christopher Dale Golden | — | (805) 648 3131 | Electricians | Ventura · Ventura County | — | — |
| Ojai Concrete | Aguero Santos Alejandro | ojaiconcrete@gmail.com | (805) 836 1975 | Other | Oak View · Ventura County | — | — |
| Ojai Construction Company | Louis Charles Hurak | — | (805) 218 2189 | GC, remodel, ADU | Ojai · Ventura County | — | — |
| Ojai Construction Pros | Donald Lee Davidson | — | (805) 798 1684 | GC, remodel, ADU | Oak View · Ventura County | — | — |
| Ojai Contracting Group INC | Evonne Louise Silvestri-Vacca | — | (805) 798 4742 | Other | Oak View · Ventura County | — | — |