HIV counseling and testing (CT) is slowly being introduced as one of several key components of the comprehensive package of HIV/AIDS prevention and care in Nigeria, particularly in the prevention of mother-to-child transmission of HIV (PMTCT). A cross-sectional survey of 804 women attending antenatal clinics (ANC) in Ogun State, Nigeria was done using questionnaires to assess their willingness to seek and undergo CT and know the determinants. Focus group discussions were also held in the general community: 84.3% of respondents believed in AIDS reality, while 24.3% thought they were at risk of HIV infection. Only 27% knew about MTCT, while 69.7% of 723 who had heard of HIV/AIDS did not know about CT. Only 71 (8.8%) had thought about CT and 33 (4.5%) mentioned HIV testing as one of antenatal tests. After health education on CT, 89% of the women expressed willingness to be tested. Their willingness for CT was positively associated with education (p < 0.05), ranging from 77% (no education) to 93% (post-secondary). More of those with self-perceived risk expressed willingness to test for HIV (p < 0.05). Those willing to be tested had a higher knowledge score on how HIV spreads than those not willing. Multiple regressions identified four key factors that were associated with willingness for CT: increasing educational level; not fearing a blood test; perception that the clinic offered privacy; and perceptions of higher levels of social support from relatives and peers. Those unwilling or undecided about CT expressed strong fear of social stigma/rejection if tested positive. The results provided insights for planning promotional programs and showed that not only are IEC efforts needed to boost knowledge about HIV/AIDS, but that change in clinic setting and community are imperative in creating supportive environment to encourage uptake of CT services.