Background: Although there are thousands of health and fitness smartphone apps currently available, little research exists regarding the effects of mobile app technology on physical activity behavior. Purpose: The purpose of this study was to test whether Exergame smartphone applications increase physical activity levels. Methods: This was a 12-week randomized, controlled, parallel group trial. The intervention consisted of the use of Exergame smartphone apps and motivational messaging. Validated instruments were used to measure physical activity, enjoyment, motivation, and competence. Results: Forty subjects were randomized and completed baseline assessments; 39 (97.5%) completed the 12-week follow-up. Median age was 32 years (interquartile range [IQR] = 25, 41.75); 85% were women. No differences between groups were identified in primary or secondary outcomes. Within group, physical activity decreased in the controls and autonomous motivation increased in the intervention group. Discussion: Exploratory findings were interesting regarding the use of Exergames to encourage physical activity. The intervention group showed less of a decline in activity, suggesting a possible attenuation of the observed seasonal fluctuation by the use of the Exergames. Translation to Health Education Practice: Given their popularity, health educators should continue to explore the use of Exergame apps as a tool to facilitate physical activity.