The present study tested the hypothesis that individual differences in autonomy or control causality orientation would moderate the undermining effect of rewards on intrinsic motivation. Equal numbers of autonomy- and control-orientated participants provided solutions to an interesting puzzle under reward or no reward conditions. Participants were then required to provide further solutions to the puzzle in a free-choice period. The time spent in solving the puzzle during the free-choice period constituted the dependent measure of intrinsic motivation. Results revealed a significant interaction effect of causality orientations and reward condition on intrinsic motivation. Control-oriented participants assigned to the reward condition exhibited significantly lower levels of intrinsic motivation compared to those assigned to the no reward condition. In contrast, there was no significant difference in intrinsic motivation levels across the reward conditions for autonomy-oriented individuals. Findings indicate that an autonomy-oriented causality orientation offered a degree of ‘protection’ from the undermining effect of rewards on intrinsic motivation. This is in keeping with self-determination theory in terms of the interactive effects of environmental events and interpersonal factors on intrinsic motivation.