Transnational migrant workers are known to be at high risk for HIV/STIs. This study estimated the point prevalence of HIV/syphilis and examined correlates of HIV/syphilis testing uptake among female migrant domestic workers in Macao, China. Data was obtained from 1363 female Filipino domestic workers who were offered free rapid HIV and syphilis testing. A mixed methods analysis was undertaken to examine correlates of testing and themes about reasons for not testing. Among 1164 women tested, there were no cases of HIV/syphilis observed and 199 (14.6%) refused HIV/syphilis testing. Greater social integration (aOR 1.12; 95% CI 1.02–1.24), having more than one sexual partner (aOR 1.65; 95% CI 1.02–2.65), and longer working hours on the testing day (aOR 0.97; 95% CI 0.94–1.00), were associated with testing uptake. Among those who tested, the majority (> 70%) had never tested before, suggesting the need to improve testing outreach. Qualitative themes about reasons for not testing included low perceived need and insufficient time. Individual and structural testing barriers should be reduced to optimize HIV/STI testing in migrant populations.