Background and objective: The COVID-19 pandemic has introduced changes in physical activity of various populations. The aim of this study was to assess the impact of the COVID-19 pandemic on physical activity in a representative sample of adult residents of Lithuania. Methods: The survey data was collected from October to November 2021. After the exclusion of missing data, this study included a representative sample of 1502 adult residents of Lithuania aged from 18 to 64 years old. The chi-square criterion was used to estimate the association between sociodemographic variables, COVID-19 experience and food selection criteria with change in physical activity during the pandemic. Results: Although the majority (54.7%) of the participants of this study indicated no effect of the COVID-19 pandemic on their physical activity, 33.8% of the sample indicated the decrease in physical activity. During the pandemic, physical activity increased among 11.4% of the respondents. Decrease in physical activity was more frequent among younger respondents (38.6% vs. 29.6%), people from the largest towns of Lithuania (39.9% vs. 29.4%), single respondents (45.7% vs. 31.2%) and those who suffered from COVID-19 personally or had COVID-19 cases in their families (28.6% vs. 41.8%) (p<0.05). Physical activity increased more frequently among respondents with university education and those who selected their foods with respect to its impact on health (respectively, 14.4% vs. 5.8% and 15.6% vs. 9.6%) (p<0.05). Gender, employment status, number of family members, having children under 18 years, monthly income per family member and severeness of COVID-19 of the respondents were not associated with changes in physical activity during the pandemic (p>0.05). Conclusions: The COVID-19 pandemic has reduced the physical activity in one third of the population of adult residents of Lithuania. The decrease was observed among both – residents with higher and lower prepandemic physical activity.