Concerning human immunodeficiency virus (HIV) epidemiology, pregnant women (PW) are particularly vulnerable and severely affected. Nigeria has over 40 years of HIV epidemiology and enlightenments; to suggest control hub, we sought to know extant variables predicting HIV positivity among PW in selected towns in Osun State. Our hypothesis: none of the study PW’s variables predicts HIV seropositivity. With from UNIOSUN Health Research Ethics Committee, 900 consecutively selected consenting PW attending antenatal care (ANC) facilities in four towns (capital city inclusive) provided relevant sociodemographic/behavioral data with questionnaire forms; each participant was aseptically bled and plasma screened with the Alere Determine Rapid HIV-1/2 Kit. The presumptive reactive plasma samples (and some randomly selected nonreactive samples) were confirmed with Genscreen ULTRA HIV-1/2 P antigen/antibody ELISA. Microsoft Excel and SPSS 16.0 were used for result analysis using -test, CHI test, and binary logistic regression. The PW were 15-50 years of age ( = 900; mean: 26.6 years [95% CI: 26.1-26.9 years]); they were predominantly 15-29 years (71.1%), married (90.8%), with one lifetime sexual partner (86.4%). Seropositive PW by screening and confirmatory tests were, respectively, 14 (1.6% [95% CI: 0.9-2.6%]) and 15 (1.7% [95% CI: 0.9-2.7%]). The latter were predominantly 20-30 years (80.0%), married (93.3%), with ≤ secondary school education (86.7%), reportedly never screened for HIV (60.0%), with 86.7% aware HIV is sexually transmitted. Analysis showed only ≥ three lifetime sexual partners was independently associated with HIV seropositivity ( = 0.03; odds ratio (OR) = 17.0). Although educational status was not associated with seropositivity, PW having primary school education had about 6 times higher likelihood of seropositivity ( = 0.06; OR = 5.7 [95% CI: 0.94-35.1]). Also, primigravida had about twice higher likelihood of seropositivity ( = 0.44; OR = 1.5 [95% CI: 0.54-4.17]). HIV seropositivity was relatively low and majorly predicted by ≥ three lifetime sexual partners; suggesting this as prime focus of HIV counseling among PW attending ANC in Osun State, Nigeria.