Abstract: In order to estsblish an urinary enzyme assay as an useful and significant clincal or investi-gative laboratory aid, the kinetics of the hydrolysis of phenolphthein mono-β-glucuronide by-G in human urine was investigated. In our study the optimum pH was 5.2 in 0.2M acetate buffer at 37℃. The substrate concentration required was found to be 3×10^-3m and the enzyme had a Michlis constant of 1.6+0.39mM (X+SD) of phenol-phthalein glucuronide. The reac-tion velocity was constant within an observation period of 4-20 hours. in addition, the absorption spectrum of phenolphthalein liberated, the effect of urine samples storage in refrigerator and reproducibility of the results were tested aiso. Urinary β-G activity was observed in 45 patients with carcinoma of urinary bladder and 56 normal subjectl. It was found that the activity of β-G in the urine was usually increased in patients with bladder carcinoma and usually decreased 1-10 months after sur-gery in 22 patients. As to the question of whether the increased β-G is due to the trigger mech-anism causing the tumor or is the consepuence of the neoplasia remains to be studied.