We evaluated the effect of a novel potent urease inhibitor, N-(diaminophosphinyl)isopentenoylamide (IPA), on the development of an infection bladder stone using our urolithiasis model in rats. IPA was excreted into urine after oral administration to rats, and the cumulative urinary recovery rate of unchanged IPA reached about 29.6% within 24 h (50 mg/kg). The oral administration of IPA (6.25 mg/kg, b.i.d., 5 d) significantly inhibited the development of the infection bladder stone. The present result suggests that IPA is a very promising compound in the prevention of formation and recurrence of an infection stone owing to a high efficacy and a low toxicity of IPA in animals.