The purpose of this study was to examine effects of positive/negative thinking on the depletion of self-regulatory resources in defensive pessimists and optimists. A laboratory experiment was conducted individually with 90 university students to investigate whether defensive pessimists or optimists exhibited different effects for depletion of resources. Results showed that when participants were instructed to engage in tasks with external pressure and given negative feedback, defensive pessimists required lower levels of self-regulation than did optimists. When participants engaged in an autonomous task and were given positive feedback, this pattern was reversed. That is, even if defensive pessimists receive negative feedback, they prepare carefully for a variety of worst-case scenarios. Therefore it is not necessary for them to expend greater resources, whereas, for defensive pessimists positive thinking does require more use of resources. Future research should examine different effects of manipulation resulting in positive or negative thinking.