Research provides increasing support of self-worth, non-physical motives, and body image for predicting physical activity in women. However, no empirical tests of these associations have been conducted. Ecological momentary assessment (EMA) has been recognized as useful for understanding correlates of physical activity. This study tested the feasibility of a novel EMA protocol and explored temporal relationships between daily self-worth and physical activity in middle-aged women. Women aged 35-64 years (N=63; M age=49.2±8.2 years) received text message prompts to an Internet-based mobile survey three times daily for 28 days. The survey assessed momentary activity, self-worth (knowledge, emotional, social, physical, general), and self-efficacy. Women concurrently wore an accelerometer on their non-dominant wrist. Feasibility was assessed via accelerometer wear-time estimates, survey completion rates, and participant feedback. Multilevel models examined the predictive influence of self-worth on daily activity counts. Self-efficacy was also tested due to known relationships with self-worth and physical activity in women. Wear time was high (952.92 ± 100.99 min per day), with only 141 observations lost to non-wear. However, 449 were lost to accelerometer malfunction. Women completed 80.8% of surveys. After excluding missing physical activity data, 67.5% of observations (N=3573) were analyzed. Although women thought the survey was easy to complete, perceptions of the accelerometer were mixed. Approximately 34% of the variance in daily counts was within individuals (ICC=0.66). Average self-efficacy (β=0.005, p=0.009), daily fluctuations in self-efficacy (β=0.001, p<0.001), and daily fluctuations in general self-worth (β=0.04, p=0.003) predicted daily activity. There were significant individual differences in relationships between daily fluctuations in emotional (β=0.006, p=0.02) and general self-worth (β=0.005, p=0.02) and daily activity. The use of text message prompts and an Internet-based mobile survey was feasible for conducting EMA in middle-aged women. Research identifying optimal methods of behavior monitoring in longitudinal studies is needed. Results provide support for small but significant associations among daily fluctuations in self-efficacy and general self-worth and daily activity in middle-aged women. The impact of emotional self-worth may differ across women. Further research examining the transient natures of self-efficacy and general self-worth, improving self-worth scales, and testing momentary strategies to increase women's self-worth and physical activity is warranted.