Indenopyridine hydrochloride (IH), an antispermatogenic agent, was tested to determine the testicular pathological changes, seminal spermatozoa concentrations and seminal plasma alkaline phosphatase levels in male dogs. A single oral dosage of 30 mg IH/kg BW induced the dissociation and premature release of germ cells into the lumens of seminiferous tubules. Ring-shaped spermatid nuclei, nuclear pykonosis of spermatocytes and multinucleated cell associations were also observed. Thereafter, the spermatogenic index (SI) significantly decreased one day after IH administration. Moreover, seminal spermatozoa concentrations decreased two weeks after drug treatment; and there was a statistically significant difference in spermatozoa production inhibited by IH compared to the control. Reversible spermatogenesis was noted 7 weeks after IH treatment in male dogs. Meanwhile, seminal plasma alkaline phosphatase levels also significantly increased two weeks after IH treatment. These data confirm that IH might induce a two-month inhibition of spermatogenesis in male dogs.