Malnutrition is prevalent among pediatric oncology patients admitted to the pediatric intensive care unit (PICU), which leads to unfavorable clinical outcomes. This was a secondary data analysis of the nutrition data of 160 pediatric oncology patients admitted to the PICU. Cox's regression (adjusted for sex, age, and pediatric critical illness score) and Chi-square were used to examine the association between nutritional status and outcomes. Most of the patients were diagnosed with leukemia and admitted to PICU for medical reasons. The prevalence of malnutrition was 11.3% according to weight-for-age z-score, 16.3% according to height-for-age z-score, 21.3% according to body mass index-for-age z-score, 14.4% according to weight-for-height z-score, 34.4% according to mid-upper arm circumference-for-age z-score. Anthropometrical parameters that predicted the duration of mechanical ventilation were weight-for-age (hazard ratio [HR], 2.727; 95% confidence interval [CI], 1.729-4.302); height-for-age (HR, 1.969; 95% CI, 1.440-2.693); weight-for-height (HR, 2.645; 95% CI, 1.575-4.441); and upper arm muscle area-for-age (HR, 2.098; 95% CI, 1.430-3.077). Length of PICU stay was predicted by weight-for-age (HR, 1.207; 95% CI, 1.014-1.436). Malnutrition is prevalent among pediatric oncology patients admitted to the PICU, which lead to unfavorable clinical outcomes. Comprehensive nutritional status assessment should be performed for these children.