Objectives Oral sex and its associated factors among low-tier female sex workers (FSWs) have not been documented in the Chinese literature. Here, we report this perspective in this group. Methods The data were derived from a large cross-sectional study conducted among low-tier FSWs using a structured questionnaire in 21 counties in Zhejiang province, China. The prevalence of oral sex and its associated factors among 2645 low-tier FSWs were analyzed using bivariate and multivariate analysis. Results Of all participants, 579 (21.9%) had performed oral sex with clients over the previous month. Multivariate analysis revealed that oral sex is related to being unmarried, low income, early initiation of commercial sex, having conducted commercial sex in more counties, longer duration of commercial sex, larger number of clients, ever having engaged in anal sex, less use of condoms and oral contraceptives during the previous month, low rate of adoption for contraception at the present time, and STI-related symptoms during the previous half year. Conclusion Oral sex practitioners among low-tier FSWs in China are at a higher risk of STI, HIV, and unwanted pregnancy compared to those who did not engage in oral sex. Behavioral interventions carried out among low-tier FSWs should specifically target low-tier FSWs who practice oral sex, should carefully take into account the characteristics of these FSWs, provide risk awareness education and training for condom use negotiation, and promote the availability of condom and reproductive health care, timely diagnosis, and treatment of STIs.