Background and aim: Physical activity (PA) can modulate the immune response, but its impact on infectious disease severity is unknown. We assess if the PA level impacts the severity of COVID-19. Methods: Prospective, cohort study for adults hospitalized due to COVID-19, who filled out the International Physical Activity Questionnaire (IPAQ). Disease severity was expressed as death, transfer to intensive care unit (ICU), oxygen therapy (OxTh), hospitalization length, complications, C-reactive protein, and procalcitonin level. Results: Out of 326 individuals, 131 (57; 43.51% women) were analyzed: age: median—70; range: 20–95; BMI: mean—27.18 kg/m²; and SD: ±4.77. During hospitalization: 117 (83.31%) individuals recovered, nine (6.87%) were transferred to ICU, five (3.82%) died, and 83 (63.36%) needed OxTh. The median for the hospital stay was 11 (range: 3–49) for discharged patients, and mean hospitalization length was 14 (SD: ±5.8312) for deaths and 14.22 days (SD: ±6.92) for ICU-transferred patients. The median for MET-min/week was 660 (range: 0–19,200). Sufficient or high PA was found in recovered patients but insufficient PA was observed in dead or ICU-transferred patients (p= 0.03). The individuals with poor PA had a higher risk of death (HR = 2.63; ±95%CI 0.58–11.93;p= 0.037). OxTh was used more often in the less active individuals (p= 0.03). The principal component analysis confirmed a relationship between insufficient PA and an unfavorable course of the disease. Conclusion: A higher level of PA is associated with a milder course of COVID-19.