PURPOSE: Malnutrition is quite prevalent in hospitalized cancer patients, with a 40%~80% rate. Malnutrition in cancer patients can result in an increase in the number of complications, length of stay, mortality, and morbidity. Therefore, cancer patients with malnutrition must have the appropriate nutritional support to improve the prognosis of cancer. This study evaluated the appropriate time point to start parenteral nutrition (PN) after admission according to the nutrition support guidance in Samsung Medical Center. METHODS: This study enrolled patients diagnosed with the Korean standard classification of disease 6 (KCD6) code C00-C97 and discharged from March 1st to 31st, 2016. The following data were collected: patients'age, gender, diagnosis, length of stay, body mass index, nutritional status, and whether to consult nutrition support team (NST). RESULTS: Among a total of 2,944 patients, 381 patients (12.9%) were in a malnourished status upon admission. In the malnourished patients, 139 patients were prescribed PN for a median of 6 days (range, 1∼49) and moderate to severe malnourished patients were started on PN within 2 days after admission. The proportion of patients with a poor nutritional status was lower in the NST group than in the non-NST group (50.0% vs. 66.7%) on the 28th day after admission. Among the nourished patients, 229 patients were prescribed PN. Of them, 183 patients (79.9%) were started on PN within 7 days after admission. CONCLUSION: In moderate to severe malnourished cancer patients, the initiation of PN on the day after admission is appropriate.