| ONESPOT 1406877 · TMA804130 · design | 2180792 Ontario Inc. | 6 Metal9 Electronics10 Medical+5 | Registered | 2011 |
| ONESPORT 2119011 · TMA1186396 · design | Dongguan onesport Technology Co. Ltd | 12 Vehicles | Registered | 2023 |
| ONSPEX 1223686 · TMA667051 · design | CANADIAN STANDARDS ASSOCIATION | 35 Advertising42 Science | Registered | 2006 |
| OMNISPORT 0439017 · TMA251317 | APT Advanced Polymer Technology Corp. | 9 Electronics22 Ropes28 Toys | Registered | 1980 |
| OMNISPORTS 1298874 · TMA743900 | Tarkett Inc. | 27 Carpets37 Construction | Registered | 2009 |
| ONESHOP 2144537 · TMA1201685 · design | Inventory Systems Inc. | 42 Science45 Legal | Registered | 2023 |
| ONESPAN 1927833 · TMA1217821 | OneSpan North America Inc. | 9 Electronics38 Telecommunications42 Science+1 | Registered | 2024 |
| ONESPIN 1279225 · TMA701725 | Siemens Electronic Design Automation GmbH | 9 Electronics41 Education42 Science+1 | Registered | 2007 |
| ONSCOPE 1160510 · TMA609316 | ONSCOPE GROUP INC./GROUPE ONSCOPE INC. | 9 Electronics16 Paper35 Advertising+1 | Registered | 2004 |
| ONESPEC 2266115 | CertainTeed LLC | 19 Building36 Finance37 Construction+2 | Pending | 2023 |
| OMOOSPACE 2210855 · TMA1226378 | Studio Grand Design Inc. | 9 Electronics | Registered | 2024 |
| oncoflake 2183708 · TMA1229630 | Oncoradiomics | 9 Electronics42 Science44 Medical | Registered | 2024 |
| OMNISHOP 2169237 · TMA1282577 | Cloud Drop Technologies LLC | 9 Electronics14 Jewellery16 Paper+7 | Registered | 2025 |
| ONCOBIX 2146652 · TMA1228857 · design | ONCOBIX CO., LTD. | 5 Pharmaceuticals | Registered | 2024 |
| ONCOPREX 2089152 · TMA1214024 | Genprex, Inc. | 5 Pharmaceuticals | Registered | 2023 |
| OMGEVI 2089065 · TMA1196487 | Theravance Biopharma Ireland Limited | 5 Pharmaceuticals | Registered | 2023 |
| OMNISPEND 2081260 · TMA1150613 | Market Track, LLC | 9 Electronics35 Advertising42 Science | Registered | 2022 |
| OMNICEPT 2060646 · TMA1278414 | Hewlett-Packard Development Company, L.P. | 9 Electronics | Registered | 2024 |
| ONECABLE 2036998 · TMA1270704 | an individual | 9 Electronics | Registered | 2024 |
| ONECABLE 2036997 · TMA1270703 · design | an individual | 9 Electronics | Registered | 2024 |
| ONCOPEPTIDES 2033388 · TMA1227653 | an individual | 1 Chemicals5 Pharmaceuticals42 Science | Registered | 2024 |
| OmegaPower 2001204 · TMA1271975 | OCEANBLUE LLC | 5 Pharmaceuticals | Registered | 2024 |
| OncoFreeze 1942178 · TMA1159644 | Siemens Medical Solutions USA, Inc. | 9 Electronics | Registered | 2023 |
| ONCOVANT 1939566 · TMA1125507 | Roivant Sciences GmbH | 5 Pharmaceuticals42 Science44 Medical | Registered | 2022 |
| OMNICABLE 1925234 · TMA1106330 | Omni Cable Corporation | 35 Advertising | Registered | 2021 |