Background: High rates of sexually transmitted infections (STIs) among men who have sex with men (MSM) have been reported, there is little research on their STI knowledge. Our study sought to characterize knowledge and awareness of STIs among MSM in Nairobi, Kenya. Methods We mobilized MSM aged ≥18 years from Nairobi into a cross-sectional study. To determine their understanding about STIs, a pre-tested structured questionnaire was administered. Knowledge score was generated by summing up the number of responses answered correctly by a participant. We dichotomized scores as “low” and “high”, by splitting the group at <12 and ≥12 which was the mean. Results A total of 404 participants were interviewed between the month of March and August 2020. The mean age was 25.2 (SD=6.4) years. Majority were single (80.4%) and Christians (84.2%). All participants had some formal education ranging from primary to tertiary; the majority (92.3%) had secondary education or more. Most (64.0%) were employed and their monthly income ranged from <50->150 USD. Almost all (98.5%) were Kenyans. Of the 404 (90.6%) self-identified as male and (47.5%) reported to be exclusively top partners. Many (39.9%) reported being both bottom and top, while those reporting to be bottom partners were, (12.6%). The last 12 months, (55.4%) of the participants reported having sex with men only and (88.6%) reported to have had more than one sexual partner. Participants scored an average of 12.2, out of 29 SD 4.5. The multivariable modelling revealed that participants aged ≥25 years were more likely to have a higher knowledge score compared with the participants aged 18-24 years (aOR=0.973, CI: 0.616-1.538). Regarding education and occupation, participants who had tertiary education and those who were employed were more likely to have a higher knowledge score compared with the participants who had primary education and were not employed ( aOR=2.627, CI:1.142-6.043) (aOR=0.922, CI: 0.401-2.117). Participants who were earning (USD >150) were more likely to have a higher knowledge score compared to the ones who were not earning (aOR=2.520, CI: 0.900-7.055). Further bisexual men were more likely to have a higher knowledge score compared with the participants who were having sex with men only (aOR= 1.550, CI: 1026-2.342) Conclusion Participant’s knowledge level regarding STIs was low. We recommend health care workers to continue educating patients about STIs.