Background Although aggressive multimodal treatment programs in childhood cancer have significantly increased survival rates, the morbidity caused by protein energy malnutrition related to therapy is still high. Objective To describe nutritional status changes in children with malignant solid tumors after 21 days of chemotherapy. Methods A descriptive prospective study with pre-and post-test design in children with malignant solid tumors was conducted in the Department of Child Health, Medical School University of Indonesia/Cipto Mangunkusumo Hospital, Jakarta between January and July 2004. Anthropometrics (body weight, BW and midupper- arm circumference, MUAC) and serum albumin measurements were performed before and after 21 days of chemotherapy. Results Twenty-two children were enrolled in this study. After 21 days of chemotherapy, 8 children had decreased BW and 6 children had decreased MUAC, but 3 children gained weight and had increased MUAC. Based on MUAC-for-age, 7 children had decreased nutritional status. Fifteen children had reduced serum albumin levels based on a 10% cut-off point. The number of children who had reduced serum albumin was larger than those who had reduced BW and MUAC. In the evaluation of average oral food consumption during 21 days, 7 out of 16 children could accept more than 2/3 portion of served food. All of the children who received enteral feeding could accept more than 2/3 portion of served food. Conclusion There was a decrease of nutritional status, BW, MUAC, and serum albumin in most of the subjects after chemotherapy. Serum albumin level measurement was the more sensitive parameter in determining nutritional status changes. Enteral feeding seems more appropriate to fulfill nutritional needs than oral feeding.