Purpose: This study was done to identify factors associated with fatigue in pediatric patients with cancer in order to develop nursing interventions for this population. Methods: The participants were 95 pediatric cancer patients admitted to a university medical center in Seoul, Korea, and 95 parents. The PedsQLTM, Multidimensional Fatigue Scale developed by Varni (2002) was used to measure fatigue. Data were analyzed with the SAS program and t-test, analysis of variance (ANOVA), Pearson correlation coefficients, and multiple regression were used to identify the association of factors with fatigue. Results: The mean score for fatigue was 30.42 in the pediatric cancer patients and 34.77 in the parents. Fatigue was higher in patients living with a single parent, in patients whose father had a lower education and those patients with a fever. Pain, frequency and intensity of nausea and vomiting, depression, anxiety, and disruption of usual activity were positively associated with fatigue. The predictive factors for fatigue were disruption of usual activity, depression and living with or without parents. Conclusion: Pediatric patients with cancer experienced fatigue during their diagnosis and treatment. Of the multiple factors associated with fatigue, the association between disruption of usual activity and fatigue was the highest indicating a need to be concerned with this factor when providing interventions to alleviate fatigue.