OBJECTIVES: The purpose of this project was to evaluate the incremental costs of increasing physical activity and improving body composition for a lifestyle walking program targeting sedentary African American women. METHODS: The Women’s Lifestyle Physical Activity Program was a randomized behavioral trial that included a group intervention with social support and culturally relevant, tailored content about increasing physical activity and an automated telephone response system to track physical activity for sedentary African American women ages 40-65. The principal outcomes were change in minutes of walking and moderate and vigorous physical activity per week, and body mass index (BMI) between baseline and 24 weeks. Incremental cost effectiveness ratios (ICER) were calculated for each outcome. The cost-effectiveness analysis included both program and participant costs and was calculated in 2013 US dollars. RESULTS: For the 260 participants in the analysis, participant costs (e.g., group session attendance, logging physical activity in the ATR system) were $152 ± 42, while program costs (e.g., group session facilitation, materials and supplies) were $164 ± 21, for a total cost of $316 ± 59. Walking increased by 200 minutes per week at 24 week, with an ICER of $1.64 (95% CI, 1.63 – 1.66) per minute, moderate and vigorous physical activity increased by 117 minutes per week, with an ICER of $2.79 per minute, and BMI decreased by 0.09 points, with an ICER of $3463 (95% CI, 500 – 9,540) per 1-point reduction.  CONCLUSIONS: The Women’s Lifestyle Physical Activity Program is a relatively low cost strategy for increasing physical activity. The incremental cost of increasing walking minutes is substantially lower than for moderate and vigorous physical activity. The participant costs related to time in the program were more than half of the total costs, suggesting that practitioners and policymakers should consider the participant cost when disseminating group programs into practice.