We developed an innovative home-based HIV self-testing (HIVST) service that included mailing of a free HIVST kit, and providing online real-time instructions and pre-test/post-test counseling (HIVST-OIC). The present parallel-group and non-blinded randomized controlled trial was conducted to evaluate the efficacy of promoting HIVST-OIC in increasing HIV testing rate among 430 men who have sex with men (MSM), with access to online live-chat applications in Hong Kong. At month 6, as compared to the control group, the intervention group reported significantly higher prevalence of HIV testing of any type (89.8 vs. 50.7%; relative risk (RR): 1.77; p < 0.001). Among those who have taken up any HIV testing in the last six months, significant between-group difference was found in multiple male sex partnerships (34.2 vs. 47.7%, RR: 0.72; p = 0.021). HIVST-OIC has a strong potential in increasing prevalence of HIV testing and reducing sexual risk behaviors. Implementation research is warranted.