Purpose: The purpose of this study was to verify the effects of gum chewing temporalis muscle exercise on masticatory discomforts after craniotomy. Methods: Data collection was performed from July 10 to October 24, 2008. Forty participants who were treated with elective craniotomy were enrolled in this study. Twenty participants in the exercise group were given a gum chewing exercise protocol for five days and twenty participants in the control group received usual postoperative care only. All the participants were examined on the first, third and fifth postoperative day regarding the masticatory pain score, mouth opening range, and satisfaction with mastication. Collected data were analyzed using t-test, $x^2$-test and repeated measures ANOVA. Result: Masticatory pain of experimental group was significantly lower than the control group ($p$ <.001). Mouth opening range and satisfaction with mastication of experimental group were significantly improved in experimental group compared with the control group ($p$ <.001). Conclusion: The gum chewing temporalis muscle exercise after craniotomy is a useful intervention to reduce masticatory pain and to improve mouth opening range, recovery rate of mouth opening range and satisfaction with mastication.