BackgroundThis study aimed to develop a unique online infection prevention and control (IPC) training on Covid-19 for healthcare workers in psychiatric institutes in Japan and to examine its efficacy based on its impact on the knowledge, attitude, and confidence about IPC for Covid-19 among the healthcare workers.MethodThis quasi-experimental study was conducted using online training on Covid-19 IPC for healthcare workers in various psychiatric institutes from April 2021 to March 2022. An online training video on Covid-19 IPC was developed. Voluntary healthcare workers in psychiatric institutes located in five prefectures in Japan were recruited to participate in this training. The participants then completed 30 min of online training and surveys about knowledge, attitude, and confidence were conducted pre, post, and three months after the training. The video training and surveys were contextually validated by the experts, but not by any previous study.ResultsA total of 224 participants were included, of which 108 (54.0%) were men. The mean (standard deviation (SD)) age and the mean occupational experience were 47.4 (9.5) and 18.0 (12.6) years, respectively. Among the participants, 190 (84.8%) completed the post-training, and 131 (58.5%) completed the three-month-later training surveys. The total score on the quizzes in the post-training (+ 31.1%, SD 15.7, p-value < 0.01) and three-month-later training (+ 14.9%, SD 16.8, p-value < 0.01) surveys had significantly increased from that in the pre-training survey. In contrast, the total score in the three-month-later training had significantly decreased from that in the post-training survey (-16.1%, SD 16.7, p-value < 0.01).ConclusionThirty minutes of online training about IPC for Covid-19 had improved knowledge, confidence, and attitude among psychiatric healthcare workers. Regular online training would help in preventing the transmission or formation of clusters of Covid-19 in psychiatric healthcare institutes.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12888-023-04826-5.