This paper reports a case of pancreatic tail cancer with peritoneal carcinosis that showed a good response to gemcitabine hydrochloride. A 52-year-old man, who had undergone a gastrojejunostomy for pancreatic tail cancer with peritoneal carcinosis, was referred to our hospital for anticancer therapy. Laboratory data on admission disclosed hypoalbuminemia and a high level of serum CA19-9 (156 IU/ml). These findings indicated that the patient was in a cancer cachexic condition. Gemcitabine hydrochloride treatment (1,000 mg/m2/week x 3/4 weeks) was started. Ascites disappeared after 2 courses of treatment, and the tumor was reduced (62% of the reduction rate) after 5 courses of treatment. Furthermore, the serum CA19-9 level and serum albumin value returned to normal, and performance status was improved to grade 1. The patient has been well for 15 months after the diagnosis of pancreatic tail cancer with peritoneal carcinosis. Gemcitabine hydrochloride may have not only reduced the tumor volume and improved cancer cachexic condition, but also prolonged the survival time in this case.