BACKGROUND: Six provinces in China accounted for 70% - 80% of all reported HIV/AIDS cases in the country in 2009 and five provinces accounted for 78% of all reported mother-to-child transmission (MTCT) of HIV cases. Because Guangxi belonged to both groups, the Prevention of Mother-to-Child Transmission (PMTCT) Plus program was established there to understand better low birth weight (LBW) and preterm delivery (PD) birth outcomes and their associated risk factors better. METHODS: Pregnancy outcomes were examined among HIV-infected pregnant women who enrolled in the PMTCT Plus program from June 2006 to February 2009 in Guangxi, China. Multivariate Logistic regression analysis was used to explore the risk factors associated with LBW (< 2500 g) and PD (gestational age < 37 weeks). RESULTS: The prevalence of LBW and PD among 194 HIV-positive mothers was 19.6% (38/194) and 9.8% (19/194), respectively. Multivariate Logistic regression analysis showed that CD4 cell count < 100 cell/µl (multivariate-adjusted odds ratio (AOR) 5.52; 95%CI 1.11 - 25.55) and CD4 cell count 100 - 199 cells/µl (AOR 3.40; 95%CI 1.03 - 11.25, compared to CD4 cell count ≥ 350 cells/µl), gestational age < 37 weeks (AOR 4.38; 95%CI 1.29 - 14.82, compared to ≥ 37 weeks), maternal weight < 45 kg (AOR 5.64; 95%CI 1.09 - 29.07) and maternal weight 45 - 54 kg (AOR 3.55; 95%CI 1.31 - 9.60, compared to ≥ 55 kg) at enrollment, and HIV RNA ≥ 100 000 copies/ml at enrollment (AOR 4.22; 95%CI 1.24 - 14.32) and 20 000 - 99 999 (AOR 2.77; 95%CI 1.01 - 7.77, compared to < 20 000 copies/ml) were associated with a higher risk of LBW. For PD, only maternal injection drug use as the route of HIV transmission (AOR 5.30; 95%CI 1.33 - 21.14, compared to those infected with HIV through sexual transmission) was significantly associated with a higher risk of PD. CONCLUSIONS: Lower CD4 cell count and higher HIV RNA viral load at enrollment were associated with LBW. Optimal antenatal care, including earlier antenatal screening and HIV diagnosis, is critical to earlier PMTCT prophylaxis and/or HIV treatment to prevent transmission of HIV to the infant and also to prevent LBW pregnancy outcomes.