| Katajavaaran metsät Oy | Agriculture & fishing | 2026 |
| Katajoki Oy | Financial services | 2021 |
| Katakombi Oy | Information & communication | 2017 |
| Katalyst Enterprise Oy | Administrative & support | 2016 |
| Katalyst Software Oy | Information & communication | 2022 |
| Katalyytti Oy | Professional & scientific | 2025 |
| Katana Creative Oy | Information & communication | 2019 |
| Katarina Tunturi Coaching Oy | Other services | 2022 |
| Katava Oy | Health & social care | 2021 |
| Katecon Oy | Construction | 2021 |
| Katharina Schmidt Studio Works Oy | Arts & recreation | 2019 |
| Kathen Yhtiöt Oy | Administrative & support | 2024 |
| Katherine Streeton Oy | Other services | 2026 |
| Kati & Reeta Avoin yhtiö | Other services | 2007 |
| Kati Malmivaara Kommandiittiyhtiö | Wholesale & retail | 1990 |
| Kati Salonen ja Mona Schalin Arkkitehdit Oy | Professional & scientific | 2003 |
| Katima Stock & Bond Oy | Financial services | 1986 |
| Katin Hoivatuki Oy | Health & social care | 2024 |
| Katin Kosmetik Oy | Wholesale & retail | 2009 |
| Katina Consulting Oy | Other services | 2017 |
| Katit Holdings Oy | Financial services | 2020 |
| Katja Alaja Creations Oy | Professional & scientific | 2009 |
| Katja Heinonen Ky | Other services | 1997 |
| Katja Kallio fcn Oy | Arts & recreation | 2009 |
| Katja Kekäle Oy | Health & social care | 2026 |
| Katja Kokko Oy | Manufacturing | 2017 |
| Katja Oksanen Oy | Health & social care | 2017 |
| KatjaVox Oy | Health & social care | 2015 |
| Katjamaria Oy | Real estate | 1977 |
| Katjanelo Oy | Real estate | 2019 |
| Katko Oy | Manufacturing | 2015 |
| Katkuru Nordic Oy | Financial services | 2019 |
| Katmoons Oy | Professional & scientific | 2022 |
| Katodi Oy | Professional & scientific | 2012 |
| Katottava Oy | Construction | 2024 |
| Katpro Oy | Construction | 2008 |
| Katrent Oy | Wholesale & retail | 2007 |
| Katri Kokki Oy | Professional & scientific | 2023 |
| KatriinaV Consulting Oy | Administrative & support | 2023 |
| Katrin valanta Oy | Education | 2026 |
| Katro Oy | Professional & scientific | 2023 |
| Katse Holding Oy | Financial services | 2022 |
| Katseen konsultit avoin yhtiö | Education | 2016 |
| Katseenvangitsija Oy | Arts & recreation | 1990 |
| Katso Merta Oy | Hospitality | 2026 |
| Katsokaa Helsinki Oy | Professional & scientific | 2010 |
| Katson Oy | Health & social care | 2017 |
| Katteeton Oy | Construction | 2014 |
| Kattiharju Wind Oy | Energy | 2023 |
| Kattilatti Oy | Professional & scientific | 2011 |
| Katto Gold Oy | Financial services | 2021 |
| Katto ja Köysi RK Oy | Construction | 2022 |
| Katto-Kodit Oy | Real estate | 2001 |
| Kattomax Rakennuspalvelu Oy | Construction | 2020 |
| Kattoturva PRO Oy | Construction | 2026 |
| Kattovalpas Oy | Construction | 2025 |
| Katu-Health oy | Health & social care | 2023 |
| KatuParkki Technologies Oy | Transport & logistics | 2025 |
| Katukapitaali Oy | Financial services | 2011 |
| Katukuva Media Oy | Professional & scientific | 2023 |
| Katuköökki Avoin yhtiö | Hospitality | 2012 |
| Katutaso-äänite Oy | Manufacturing | 2017 |
| Katzahair Oy | Other services | 2012 |
| KauGu Oy | Arts & recreation | 2023 |
| Kauanmusic Oy | Arts & recreation | 2024 |
| Kauas Creative Oy | Professional & scientific | 2015 |
| Kauas Software Oy | Information & communication | 2026 |
| Kauhajoen Hoiva ja Huolenpito Oy | Health & social care | 2013 |
| Kaukaa Oy | Professional & scientific | 2017 |
| Kaukaan Voima Oy | Energy | 2002 |
| Kaukalo Solutions Oy | Information & communication | 2017 |
| Kauko Luhtala Oy | Wholesale & retail | 1977 |
| Kaukoravintolat Group Oy | Professional & scientific | 2016 |
| Kaukoravintolat Kiinteistöt Oy | Real estate | 2025 |
| Kaukoravintolat Oy | Hospitality | 2001 |
| Kaukosuo Group Oy | Transport & logistics | 2024 |
| Kaukoviisas Oy | Professional & scientific | 1988 |
| Kaulbars Oy | Other services | 2023 |
| Kauneudella Oy | Other services | 2021 |
| Kauneus- ja hyvinvointikeskus Félicité Oy | Other services | 2008 |
| Kauneushoitola Ad Gloriam Oy | Other services | 2018 |
| Kauneushoitola Luna Oy | Other services | 2010 |
| Kauneushoitola Mervi Lindroos Ky | Other services | 1995 |
| Kauneushoitola Nana Daniela Oy | Other services | 2020 |
| Kauneusholding Oy | Health & social care | 2021 |
| Kauneuskeidas Heidi K. Oy | Other services | 2015 |
| Kauneuskeskus Maarit Renfors Oy | Other services | 2008 |
| Kauneuskeskus Sannukka Oy | Other services | 1993 |
| Kauneuspilkku Helsinki Oy | Other services | 2018 |
| Kauneuspiste Sinikka | Other services | 2011 |
| Kauneuspuoti & Kampaamo Villi Vadelma Oy | Other services | 2023 |
| Kaunis Aamu Oy | Financial services | 2003 |
| Kaunis Kaniini Oy | Education | 1993 |
| Kaunis Kyllikki Oy | Other services | 2025 |
| Kaunispään Viima Oy | Hospitality | 2019 |
| Kaunisranta Osakeyhtiö | Real estate | 2009 |
| Kauniste Finland Oy | Professional & scientific | 2008 |
| Kauno Helsinki Oy | Other services | 2019 |
| Kaunokaiverrus Oy | Wholesale & retail | 2005 |
| Kaunokki Oy | Other services | 2020 |