Due to the COVID-19 pandemic during spring semester 2020, teachers and students were forced to engage in online instruction. However, there is little evidence on the feasibility of online physiology teaching. This study demonstrated a 3-wk preliminary online physiology course based on Rain Classroom assisted by the mobile application WeChat. Eighty-seven nursing undergraduate students attended an online physiology course during the spring semester of the 2019-2020 academic year from March 9 to March 29. We determined the effects of the online physiology learning based on in-class tests, preclass preparation, and review rates for the course materials. We also measured the students' perceptions and attitudes about online learning with a questionnaire survey. Posttest scores from the first week to the third week in online physiology course (7.22 ± 1.83, 7.68 ± 2.09, and 6.21 ± 2.92, respectively) exceeded the pretest scores (5.32 ± 2.14, 6.26 ± 2.49, and 3.72 ± 2.22, respectively), and this finding was statistically significant (all P < 0.001). Moreover, the pretest scores were significant positive predictors of final grade (all P < 0.01). In addition, the percentage of preclass preparation increased in 3 wk, from 43.68% to 57.47% to 68.97%. From the first week to the third week, the review rate increased from 86.21% to 91.95%; however, the second week was the lowest of all (72.41%). Finally, students' perceptions about their online physiology learning experiences were favorable. In conclusion, online physiology instruction based on Rain Classroom assisted by WeChat was an effective strategy during the COVID-19 pandemic.