Background: Positive affective (i.e., emotional) response to physical activity is considered a key reinforcement process underlying motivation to engage future activity. However, affective response to physical activity is typically examined under controlled laboratory conditions. To understand how affective responses to physical activity may differ across naturalistic settings, this study used Ecological Momentary Assessment (EMA): Methods: Participants included 117 adults (M = 40.3 years, 73% female) who completed 32 EMA surveys by mobile phone at random times across four days. Each EMA survey asked respondents to report their current activity type (e.g., watching TV, physical activity/exercise), social context (e.g., alone, with spouse, with friends), and perceptions of their current setting (e.g., greenness, safety, traffic, shade, litter). Participants also rated their current mood and enjoyment. Analyses only included observations where physical activity/exercise was reported as the current activity (n=218). All models controlled for age and gender. Results: Enjoyment of physical activity was significantly greater when it occurred with a spouse, child, or other person present as compared with being alone (F = 3.10, p = .023). In settings where participants perceived greater greenness (i.e., trees, plants), they reported significantly greater enjoyment (β= .476, p = .013) and positive mood (β= .489, p = .012) during physical activity. Conclusion: Contextual features of physical activity settings may enhance affective response. Motivation to engage in future physical activity may be reinforced by encouraging adults to be physically active in the company of other people and in outdoor settings with higher levels of greenness and vegetation.