Purpose: The purpose of this study was to identify the relationship between physical activity and fatigue in patients with cancer. Methods: The participants of the study were 118 patients who had been diagnosed with cancer at least more than three months before at a university hospital. Physical activity was measured by IPAQ Korean version (2006), and fatigue by the Revised Piper Fatigue Scale. The collected data were analyzed using frequency, percentage, t-test, ANOVA, Pearson correlation coefficient. Results: Continuous physical activity overall in this study was on average $2,154.03{pm}2,845.86$ MET, and the overall degree of fatigue of the participants was $4.47{pm}1.80$. There were significant negative correlations between fatigue and moderate physical activity. Conclusion: The findings of the study suggested that moderate physical activity is effective for improving fatigue in cancer patients.