The advent of Anti-Retroviral Therapy (ART) has resulted in remarkable improvement in the management of Human Immuno-deficiency Virus (HIV) and Acquired Immune Deficiency Syndrome (AIDS). Adherence to ART and other HIV and AIDS treatment modalities amongst HIV seropositive mothers has resulted in a reduction in the rate of Mother-To-Child Transmission (MTCT) of HIV. Nonetheless, MTCT of HIV rates remain high in Homa Bay County, Kenya, with 8.8% MTCT of HIV. This rate is higher than the World Health Organization (WHO) target of reducing MTCT of HIV to less than 5%. The study assessed maternal determinants of Prevention of Mother-to-Child Transmission (PMTCT) of HIV among HIV seropositive women on PMTCT follow-up at Homa Bay County Referral Hospital. An analytical cross-sectional design was used on a total of 274 women recruited in the study. A structured questionnaire assessed for maternal-related factors associated with PMTCT outcomes. Data on PMTCT outcomes were abstracted from files of HIV Exposed Infants (HEI) whose mothers were enrolled in the study. A total of 273 participants completed the study (response rate: 99.6%). The mean age of the study participants was 32.16 (± 5.54 SD). There was a significant association between maternal factors, reason for missed clinic visit, missed ART intake, reasons for missed ART intake, and missing to provide ART prophylaxis to infant/child and PMTCT outcome at α ≤ 0.05 (p = 0.002, p = 0.005, p = 0.006, and p = 0.05, respectively). Reason for missed clinic visit and reason for missed ART intake demonstrated 5.1 and 5.8 times increase in odds of determining PMTCT outcome (OR = 5.122, 95% CI: 0.139-189.53; p = 0.002) and (OR = 5.751, 95% CI: 0.615-53.781; p = 0.006), respectively. Maternal factors attributable to the reason for missed clinic visits and the reason for missed ART intake were the main determinants of PMTCT outcomes; hence, they are essential in the development of intervention strategies to mitigate MTCT of HIV