OBJECTIVES: Sexual health knowledge among international students in Australia is lower than domestic students, however, little is known about what factors affect the uptake of STI testing, nor if there are differences for overseas-born domestic students. METHODS: We included sexually active respondents from a survey of university students in Australia (N = 3,075). Multivariate regression and mediation analyses investigated associations of STI and HIV testing with STI and HIV knowledge respectively, sexual risk behaviour and demographics, including comparisons among: domestic Australian-born, domestic overseas-born, and international students. RESULTS: STI and HIV knowledge was positively associated with STI and HIV testing respectively (STI OR = 1.13, 95% CI: 1.09, 1.16; HIV OR = 1.37, 95% CI: 1.27, 1.48). STI knowledge was significantly lower for international than domestic Australian-born students (10.8 vs. 12.2 out of 16), as was STI testing (32% vs. 38%); the difference in knowledge accounted for half the difference in STI testing rates between these two groups. International students from Southern Asia, and Eastern Asia reported the lowest STI testing rates. HIV testing was highest amongst international students from Africa and North America. Higher sexual risk behaviour, younger age, and identifying as gay or bisexual were positively associated with higher STI and HIV testing rates. CONCLUSIONS: Our study supports greater investment and commitment by universities for the provision of sexual health education that can promote access to testing to improve the health of their students.