Rash is a common side effect of pemetrexed(PEM). In clinical trials overseas, patients were prescribed with dexamethasone(DEX), as a prevention against skin rash. Four mg of DEX was orally administered twice daily on the day prior to, day of,and day after the infusion of pemetrexed. The results showed suppression of the incidence and severity of rash. However, the dosage and period of medication was not fully verified. A recent survey was conducted retrospectively, with 81 patients who started PEM monotherapy from May 2009 to August 2010, to study the effectiveness of steroid rash prevention. The patients were classified into the non-administered group(47 patients), who were not given DEX, and the prophylaxis group(34 patients), who were given a median dose of DEX(2mg×3 days). The incidence of rash in the non-administered group was 36.2%, and 23.5% for the prophylaxis group. The severity of rash for the non-administered group was G1: 27.7%, G2: 8.5%; and for the prophylaxis group it was G1: 20.6%, G2: 2.9%. The incidence and severity of rash of the prophylaxis group was statistically and significantly lower than that of the non-administered group. This study shows that a small dosage of steroid is a possible precautionary or preventive measure for rash. Therefore, in order to reduce the incidence and severity of rash, a study with higher doses of medication similar to the clinical trials overseas should be conducted.