Objective: This study examined the effectiveness of a fully automated web-based program to increase physical activity in adults with Type 2 diabetes. Methods: Between May and July 2010, participants were randomly allocated into either a 12-week intervention (n=195) or a control (n=202) group. Participants Adults diagnosed with Type 2 diabetes, residing in Australia. Participants were assessed at baseline, 12 and 36-weeks. The primary physical activity outcome was self-reported minutes of total physical activity.Secondary physical activity outcomes included minutes spent walking, and engaged in moderate, and vigorous physical activity. Additional measures included website satisfaction and website usage. The intervention consisted of a 12-week web-based physical activity intervention developed based on the Theory of Planned Behavior and self-management framework. Data were analysed from 2011 to 2012. Results: There was a significant group-by-time interaction (X2 (df=1)=6.37, = p < .05) for total physical activity favouring the intervention group d = 0.11, for those who completed the intervention, however this was not significant in the intention-to-treat analysis d = 0.01. The intervention yielded high website satisfaction and usage. Conclusions: In general, there is some evidence for the effectiveness of web-based interventions for improving physical activity levels; however it is clear that maintaining improvements remains an issue.