Introduction: Key Populations are disproportionately affected by HIV/AIDS in all settings. Unfortunately, reaching KPs with HIV intervention is a huge challenge because of stigma, discrimination, violence, and criminalization of KPs lifestyles. Because of lack of KP specific interventions, data on KPs ART outcomes is lacking. This study determined ART outcomes among KPs 6-months after initiation. Methodology: The study was a longitudinal study of all HIV positive KPs initiated on ART in 7 One-Stop-Shops from October 2016-March 2017. Both Time-1 and Time-2 data were abstracted from facility record after initiation and 6-month after for each patient. Data abstracted include: age, sex, marital status, educational level, employment status and ART outcome 6 months after initiation. Results: Sixty-seven percent of patients were retained on ART, 1.8% died, 20.6% were lost to follow up, 4.5% transferred to other facilities and 6.2% stopped ART by the end of the 6 th month. PWID had highest retention rate (74.6%) more than MSM (70.2%), while FSW had the least retention rate (65.4%) but highest transfer out rate (4.9%) more than MSM (4.7%). Factors positively associated with retention at 6 th months include: Being a male P=0.007; higher education P=0.000; employed patient P=0.000; living with sex partner P=0.000. Conclusion: This study has laid a baseline data for ART outcomes among KPs in Nigeria. Further study is however required to identify factors that could improve retention on ART among KPs. This is important if we must achieve the second and third 90s of UNAIDs 90.90.90 goals.