Outbreaks of hepatitis A virus (HAV) infection have been occurring among men who have sex with men (MSM) in Asia-Pacific region, the United States, and several European countries since June 2015, and recently among persons who are homeless and use illicit drugs in the US. We evaluated the serologic responses and effectiveness of HAV vaccination in HIV-positive individuals during the outbreak in Taiwan. From June 1, 2015 to September 30, 2016, anti-HAV IgG was prospectively determined among all HIV-positive individuals. We prospectively observed 1533 HAV-seronegative, HIV-positive individuals (94.1% being MSM and a median CD4 count of 550 cells/µL) who were advised to receive two doses of HAV vaccines administered at six months apart. Of them, 1001 individuals (65.3%) received at least one dose of HAV vaccine during the study period and 532 (34.7%) declined to receive vaccine. The primary endpoints were serologic response at weeks 28-36 and acquisition of HAV infection during follow-up. The incidence rate of acute HAV infection was 3.7 and 99.3 per 1000 person-years of follow-up in vaccinated and unvaccinated groups, respectively, resulting in vaccine effectiveness of 96.3%. At weeks 28-36, the seroconversion rate was 63.8% and 93.7% in the intention-to-treat and per-protocol analysis, respectively. The factors associated with seroconversion at weeks 28-36 were younger age (per one-year decrease, AOR, 1.08; 95% CI, 1.02-1.12) and undetectable plasma HIV RNA load (AOR, 3.19; 95% CI, 1.32-7.68).