Depression is a significant public health problem that decreases quality of life, declines functional capacity, increases morbidity and causes costs for the society. Physical activity (PA) has been shown to prevent depressive symptoms and decrease the symptoms among slightly depressive individuals. Depressive individuals seem to be more sedentary and physically less active than those who are free of the symptoms. The purpose of the study was to examine the association between depressive symptoms measured by a modified Patient Health Questionnaire (PHQ-9) and accelerometer-based sedentary behavior (SB) and PA among 20–69-year-old Finnish adults. The study is based on the FinFit 2017 population-based study, in which depressive symptoms were assessed via modified PHQ-9 and SB and PA were measured by a tri-axial accelerometer (UKK RM42, UKK Terveyspalvelut Oy, Tampere) for seven consecutive days (24/7). Modified PHQ-9 was answered by 2191 participants and 1785 individuals used the accelerometer for at least four days during the week. 1641 participants (60 % women) answered the PHQ-9-questionnaire and used the accelerometer. The mean age of the participants was 49,4 years (standard deviation 13,4 years). Cronbach alfa of the nine items of the modified PHQ-9 was 0,87 indicating good consistency. Correlations with quality of life assessed by Rand-36 were statistically significant and ranged from -0,30 (physical functioning and pain) to -0,76 (emotional wellbeing). Higher total score in modified PHQ-9 indicated higher level of depressive symptoms. The mean total score was 6,2 points (standard deviation 4,5; range 0–25 points). Women scored on average statistically significantly higher than men. Participants spent on average 9 hours 16 minutes per day in SB, 1 hour 59 minutes standing still, 3 hours 39 minutes in light PA ja 45 minutes in moderate-to-vigorous PA. Higher score of depressive symptoms was statistically significantly associated with less standing still and less PA, assessed in terms of daily number of steps and time spent in light PA and moderate-to-vigorous PA. The associations remained statistically significant when the total score of the modified PHQ-9 was categorized in to two groups (cut-point 7). Bout lengths of SB and PA did not differ between the groups. Participants with depressive symptoms had statistically significantly less moderate-to-vigorous PA regardless of the bout length. It is important to identify depressive symptoms of the population as early as possible. Modified PHQ-9 can serve as a feasible and valid method for this purpose. Identification of the early signs of the symptoms is especially important to be able to target preventive functions, including PA promotion, appropriately.