Little is known about the information on sexually transmitted disease (STD)/AIDS in the population working in congregating trading markets in China. A cross-sectional study was conducted among three big congregating trading markets in Hefei City. Seven hundred fifty-two market vendors completed a questionnaire, 333 of two markets provided specimen for STD/HIV testing. The majority of market vendors in China are sexually active youths and adults, and have little education. The market vendors had poor knowledge of STD/AIDS. The rates of correct answers to questions about STD/AIDS varied between 21.1%-81.9%. More than 50% of the market vendors had a negative attitude toward HIV-infected individuals. Among the subjects, 27.6% had had premarital or extramarital sex; 15.9% reported using condoms in the past 12 months. Among those who provided specimens, 3.9% were identified with STD, approximately 9 times higher than that in the general population of Hefei (0.4%). Our study suggests China should implement STD/HIV prevention interventions for market vendors to prevent STD/HIV infection.