Purpose: The purpose of this study was to determine the effect of acute bouts of moderate- and high-intensity walking exercise on nonexercise activity thermogenesis (NEAT) in overweight and obese adults. Methods: Sixteen participants performed a single bout of either moderate-intensity walking exercise (MIE) or high-intensity walking exercise (HIE) on two separate occasions. The MIE consisted of walking for 60 min on a motorized treadmill at 6 kmIhj1. The 60-min HIE session consisted of walking in 5-min intervals at 6 kmIhj1 and 10% grade followed by 5 min at 0% grade. NEAT was assessed by accelerometer 3 d before, on the day of, and 3 d after the exercise sessions. Results: There was no significant difference in NEAT vector magnitude (counts per minute) between the preexercise period (days 1-3) and the exercise day (day 4) for either the MIE or the HIE protocol. In addition, there was no change in NEAT during the 3 d after the MIE session; however, NEAT increased by 16% on day 7 (postexercise) compared with the exercise day (P = 0.32). However, during the postexercise period after the HIE session, NEAT was increased by 25% on day 7 compared with the exercise day (P = 0.08) and by 30%-33% compared with the preexercise period (days 1, 2, and 3; P = 0.03, 0.03, and 0.02, respectively). Conclusion: A single bout of either MIE or HIE did not alter NEAT on the exercise day or on the first 2 d after the exercise session. However, monitoring NEAT on a third day allowed the detection of a 48-h delay in increased NEAT after performing HIE. A longer-term intervention is needed to determine the effect of accumulated exercise sessions over a week on NEAT.