The majority of North American women are insufficiently active. Using an ecological approach to examine physical activity behavior in a sample of middle-aged and older women, this study aimed to (1) describe barriers to physical activity behavior change as well as environmental characteristics present in their neighborhoods, (2) examine relationships between barriers and physical activity behavior change, and (3) investigate environmental characteristics that may contribute to physical activity behavior change. Participants were 149 women ranging in age between 39 and 68. At Time 1, self-reported physical activity was assessed. Six months later (Time 2), barriers and environmental characteristics were measured, and physical activity was re-assessed. The most prevalent barriers were daily activities and fatigue. Over time, inactive women reported higher levels of barriers (e.g. fatigue, lack of interest in physical activity) than women who remained active or increased their physical activity level. Certain environmental characteristics (e.g. enjoyable scenery, seeing others exercising in their neighborhood) are suggested as potential contributors to physical activity behavior change.