We examine serum level of galectin-3 in patients with bladder cancer. We used serum samples of 67 patients with urological diseases and classified these patients into bladder cancer group (n=43) and control group (n=24). Galectin-3 concentration was measured by ELISA (Human Galectin-3 Assay Kit, IBL). And we selected the patient with high serum galectin-3 concentration (Urothelial Carcinoma, G3, pT3a pN0M0), we performed immunohistochemical staining with the VECTASTAIN ABC (Avidin Biotinylated enzyme Complex) system. Median value of serum galectin-3 concentration was 1068 pg/ml (range 551-2028) in the cancer group vs 584 pg/ml (range 259-1262) in controls. Serum galectin-3 concentration of the bladder cancer patients was statistically higher than that of controls (p<0.0005). There was no apparent correlation in serum galectin-3 concentration with the clinico-pathological features such as stage and grade. Higher expression of galectin-3 was observed in bladder cancer tissue than in normal bladder tissue. We suggest the measurement of serum galectin-3 is useful for diagnosis of bladder cancer.