Abstract: Objective To understand the epidemiological characteristics of HIV/AIDS cases in adult females in China, and explore the potential related factors. Methods Demographic and behavioral information were collected from the newly diagnosed cases in women aged 15 years in China during 2011-2015 to analyze the main transmission modes and the epidemic trend. Results The number of newly diagnosed cases in adult females increased during 2011-2015.Most of them were transmitted by heterosexual behaviors, especially extramarital heterosexual behaviors, with the proportion increased annually. Since 2012, women aged 40-94 years have become the main population affected. Both extramarital infections and marital infections, including those in regular sex partners, accounted for high proportions. The case number and its constituent were stable in women aged 40 years, but the cases in age group 20-24 years began to decline. Extramarital heterosexual behavior was the major transmission route. Conclusion The newly diagnosed HIV/AIDS case number in adult females peaked gradually in older population, indicating the importance of HIV/AIDS prevention and control in old women by expanding the detection coverage for early diagnosis of the cases and avoiding passive infection in women.