<p>A systematic review of the effects of water immersion thermotherapy (WIT) on sleep quality in healthy adults. A comprehensive search was conducted in PubMed, Cochrane Library, Web of science, Embase, Scopus, Ovid MEDLINE, Wiley Online Library, PEDro, CNKI, SinoMed and Yiigle databases. A meta-analysis method was adopted to evaluate the improvement of sleep quality by using WIT. By calculating the standardized mean difference (SMD) and its 95% confidence interval (CI), and selecting either a common effects model or a random effects model for data pooling and analysis. A total of ten randomized controlled trials were included in this study. The results showed that WIT significantly increased total sleep time (SMD = 0.63, <i>P</i> = 0.0438) and significantly improved sleep efficiency (SMD = 0.64, <i>P</i> = 0.0419). However, there were no significant effects on sleep latency (<i>P</i> = 0.0877) or the pittsburgh sleep quality index (PSQI). Furthermore, there were no significant effects on PSQI-total score (<i>P</i> = 0.1136), PSQI-subjective sleep quality (<i>P</i> = 0.3721), PSQI-sleep latency (<i>P</i> = 0.0864), PSQI-sleep duration (<i>P</i> = 0.1402), PSQI-sleep efficiency (<i>P</i> = 0.6793), PSQI-sleep disturbances (<i>P</i> = 0.0580), PSQI-use of sleep medication (<i>P</i> = 0.9991), or PSQI-day time dysfunction (<i>P</i> = 0.6525) among the various indicators of the PSQI. WIT can significantly prolong total sleep time and improve sleep efficiency, but has no significant effect on the improvement of subjective sleep quality, indicating that the sleep-improving effect of WIT has certain limitations.</p>