Currently, 85% of Canadian adults do not meet physical activity (PA) guidelines. PA mobile health interventions have the potential of reaching a large audience, and provide opportunity for self-monitoring and associated real-time feedback. Self-monitoring has been demonstrated to be a crucial self-regulatory skill in past PA interventions (Michie, et al., 2009; Greaves et al., 2011). Motivation Engine (ME) is a newly developed mobile application that allows individuals to self-monitor PA behaviour, and uniquely provides tailored feedback to the user through the use of an online PA counselor. The purpose of this feasibility trial was to examine the utility of a PA mobile health self-monitoring application specifically designed to bolster accountability and rapport to an online PA counselor. It was hypothesized that access to this application would lead to greater increases in PA behaviour over 8 weeks in a fitness facility when compared to individuals who did not have access. Forty members of a YMCA fitness facility were randomly assigned to use of the ME (EXP; n = 21) or no access to ME (CONTROL; n=19). The study associated counselor assisted in the development of personalized PA frequency goals to be tracked daily for 8 weeks by participants, and provided tailored feedback for the study duration. Of the 40 individuals recruited (Mage=38), 32 participants (24 female, 8 male) provided follow up information at week 8. Self-reported PA at baseline and week 8 were assessed using the Godin Leisure Time Exercise Questionnaire. Repeated measures ANOVA revealed a significant time x condition interaction, such that individuals using ME were engaging in significantly more strenuous and moderate bouts of PA (7.59 bouts/week) as compared to individuals not using ME (3.58 bouts/week; p = .003). These results provide preliminary support for the utility of a mobile platform to increase PA levels in healthy adults.