The aim of this study was to estimate the contribution of genetic and environmental influences on motives for engaging in leisure-time physical activity. The participants were obtained from the FinnTwin16 study. A modified version of the Recreational Exercise Motivation Measure was used to assess the motives for leisure-time physical activity in 2542 twin individuals (mean age of 34.1 years). Linear structural equation modeling was used to investigate the genetic and environmental influences on motive dimensions. The highest heritability estimates were found for the motive dimensions of "enjoyment" [men 33% (95% CI 23-43%), women 53% (95% CI 45-60%)] and "affiliation" [men 39% (95% CI 0.28-0.49%), women 35% (95% CI 0.25-0.43%)]. The lowest heritability estimates were found for others' expectations [men 13% (95% CI 0.04-0.25%), women 15% (95% CI 0.07-0.24%)]. Unique environmental influences explained the remaining variances, which ranged from 47% to 87%. The heritability estimates for summary variables of intrinsic and extrinsic motives were 36% and 32% for men and 40% and 24% for women, respectively. In conclusion, genetic factors contribute to motives for leisure-time physical activity. However, the genetic effects are, at most, moderate, implying the greater relative role of environmental factors.