Purpose: The aim of this study was established how does exercise at different times of the day influence quality of sleep and mood. Methods: Data was collected from 18 young adults (age range: 18-27), 13 females and 5 males. A randomised crossover design was applied, and participants were randomly assigned to AB/BA treatment. Treatment A dictated exercise on every other day in the morning (until 2 p.m.), while during treatment B exercise was performed in the evening (after 9 p.m.). Indicators of quality and quantity of sleep were measured using Fitbit Charge 3 activity and sleep monitor (Google Fitbit, USA) throughout 14 consecutive days and nights. Parameters of sleep assessed in this study were total sleep time, wake time after sleep onset, sleep efficiency and duration of deep sleep. In, addition, subjective assessment of sleep quality was done every morning using The Groningen Sleep Quality Scale, while at the same time the PANAS questionnaire was used to evaluate the mood of the participants. Student T – test for dependent samples was applied for determining differences between individual parameters of sleep and mood in different treatment periods and to compare days with exercise versus days without exercise. Results: Analysis showed that none of the parameters of quality and quantity of sleep were significantly affected by the timing of exercise. There were no significant differences noticed in objective or subjective parameters of sleep quality and quantity between two cycles of exercises. Also, no significant effect of exercise on mood was recorded, in any of the exercise treatments. Conclusion: The results of this research show that there is no direct connection between exercise time and sleep quality, as well as connection between physical activity and mood. Future research should focus on extending the duration of the trial, and account for various sleep disruptors which should be controlled as much as possible.