The authors of this study examined within-person associations of environmental factors (weather, built and social environmental barriers) and personal factors (daily hassles, affect) with moderate-to-vigorous physical activity (MVPA) and sedentary behavior (SB) in African American women aged 25-64 years living in metropolitan Chicago (n = 97). In 2012-13, for seven days, women wore an accelerometer and were signaled five times per day to complete a survey covering environmental and personal factors on a study-provided smartphone. Day-level measures of each were derived, and mixed regression models were used to test associations. Poor weather was associated with a 27.3% reduction in daily MVPA. Associations between built and social environmental barriers and daily MVPA or SB were generally not statistically significant. Negative affect at the first daily signal was associated with a 38.6% decrease in subsequent daily MVPA and a 33.2-minute increase in subsequent daily SB. Each one-minute increase in MVPA during the day was associated with a 2.2% higher likelihood of positive affect at the end of the day. SB during the day was associated with lower subsequent positive affect. Real-time interventions that address overcoming poor weather and negative affect may help African American women increase MVPA and/or decrease SB.