Objectives: To examine the effect of large-scale repair work on indoor formaldehyde (FA) levels and subjective symptoms in medical students during a gross anatomy dissection course. Methods: We measured the indoor FA levels, room air temperature, and room humidity during a gross anatomy dissection course. In addition, the prevalence of subjective symptoms, keeping allergy state, and wearing personal protective equipment were surveyed in two groups of students using a self-administered questionnaire. Results: The mean indoor FA levels before and after repair work were 1.22 ppm and 0.14 ppm, respectively. The mean indoor FA level significantly decreased after repair work. The prevalences of most subjective symptoms before the anatomy practice were similar before and after the repair work. However, the prevalences of most subjective symptoms during the anatomy practice were lower after the repair work. Conclusions: The mean indoor FA levels and prevalences of subjective symptoms decreased after the repair work. We have to continuously monitor indoor FA levels, carry out private countermeasures to minimize exposure to FA, and maintain equipment for ventilation to be able to conduct practice in a comfortable environment.