Objective: To understand the confidence-related factors of refusing unprotected sex behavior among college students in Zhejiang province. Methods: Stratified cluster random sampling method was conducted among college students from 13 colleges and universities in Zhejiang province, from October to November, 2018. A total of 3 718 students who self-reported "ever having had sexual contacts" were enrolled. Chi-square test was used to compare the confidence of rejecting unprotected sex under different demographic characteristics, sexual attitude/behaviors and different intervention approaches. Multivariate logistic regression model was used to analyze the related factors. Results: A total of 3 718 college students were involved in this study with average age as (20.17±1.38) years old and 70.5% (2 620/3 718) were male. The proportions of having confidence to refuse unprotected sex behavior were 74.9% (1 963/2 620) of male and 77.9% (896/1 098) of female students, respectively. According to the results from multivariate logistic regression analysis, factors that related to the confidence of refusing unprotected sex behavior in male students would include, did not accept casual sex behavior (compared with accepted students, OR=2.247, 95%CI: 1.828-2.762), did not accept homosexual behavior (compared with accepted students, OR=1.810, 95%CI: 1.302- 2.516), having casual sex behavior in the past one year (compared with having no sex behavior, OR=1.345, 95%CI: 1.051-1.721), aware of the availability of HIV self-test reagents service in college (compared with did not knew, OR=1.381, 95%CI: 1.011-1.887), having taken the HIV infection risk self-assessment in college (compared with did not take, OR=1.707, 95%CI: 1.374-2.121). In female students, the factors would include: being urban resident (compared with rural residence, OR=1.816, 95%CI: 1.225-2.693), 21 years old or above (compared with 20 years old or below, OR=1.469, 95%CI: 1.075-2.007), having taken the HIV infection risk self-assessment in college (compared with did not take, OR=1.597, 95%CI: 1.093-2.333), etc. Conclusions Both male and female college students had higher confidence in refusing unprotected sex behavior. For male students, refusing casual or homosexual contacts, having casual sex in the recent year, knowing HIV self-test reagents service and having had HIV-related risk self-assessment in college as related factors. However, for female students; city residence, 21 years old and above, and having a HIV infection risk self- assessment in college appeared as related factors. Sexual health education should be strengthened to reduce unprotective sex behavior and to promote HIV infection risk self-assessment among the college students.