This study assessed individual-level effects of adding micro-enterprise services to a peer-mediated HIV/AIDS intervention among 227 female sex workers (FSWs) in Kenya. Survey data were collected in May-July 2003 and July-August 2005. Two-thirds of participants had operational businesses by end-line survey. Nearly half reported to have stopped sex work. Self-reported weekly mean number of all sexual partners changed from 3.26 (SD 2.45) at baseline to 1.84 (SD 2.15) at end-line survey (P < 0.001). Weekly mean number of casual partners did not change significantly. Weekly mean number of regular partners changed from 1.96 (SD 1.86) to 0.73 (SD 0.98) over the follow-up period (P < 0.001). Consistent condom use with regular partners increased by 18.5% and remained above 90% with casual partners. Micro-enterprise services may empower FSWs by giving them an alternative livelihood when they wish to exit or reduce reliance on sex work. Determinants of successful business operation by FSWs deserve further research.