Background: Although the restrictions on outings owing to the Coronavirus Disease 2019 (COVID-19) pandemic negatively affected older adults, only a few reports on observed changes in body composition and physical function owing to the pandemic. Therefore, this study examined the effects of behavioral restrictions associated with the state of emergency declaration owing to the COVID-19 pandemic on instrumental activities of daily living (IADL), body composition, and physical functions in community-dwelling older women. Methods: The analyses included 17 women who completed IADL, body composition, and physical function measurements on each measurement day before the COVID-19 pandemic (pre-COVID-19, May 2019) and after lifting the emergency declaration (during-COVID-19, December 2020). The Japanese version of the Frenchay Activities Index (FAI) was used to assess the participants' IADL. Body composition was measured as body fat percentage and whole-body muscle mass. A battery of physical tests was completed to assess participants' physical functions. The Wilcoxon signed-rank test was used for the comparison of pre- and during-COVID-19 pandemic. Results: The FAI decreased during-COVID-19 compared to pre-COVID-19 phase (p < 0.001), especially for outdoor and hobby activities. Body fat percentage increased (p = 0.004), and whole-body muscle mass decreased (p = 0.001). The sit-and-reach test decreased (p = 0.041), and the 10-meter normal walking time increased (p = 0.002). Conclusions: This study revealed that behavioral restrictions due to the COVID-19 pandemic adversely affected IADL, body composition, and physical functions of community-dwelling older women