Two cases of double primary malignant neoplasm of renal cell carcinoma and gastric cancer are presented. Case 1 was a 59-year-old woman with right renal cell carcinoma (granular cell subtype) and gastric cancer (poorly differentiated adenocarcinoma). Case 2 was a 72-year-old man with left renal cell carcinoma (clear cell carcinoma) and gastric cancer (tubular adenocarcinoma). In both cases, the occult blood reactions of stool was strong and clear gastrointestinal symptoms developed. In these 2 cases of synchronous double cancer, gastrectomy following nephrectomy was performed in the same operation.