Abstract: Valerian (a natural psychotropic) has world-wide folkloric significance as anti-anxiety and a tranquilizing herbal drug. In view of its immense use and a paucity of literature on its toxicity, valerian was evaluated for its effects on spermatogenesis, genotoxicity, reproduction and biochemical changes in male Swiss albino mice. The mice were orally treated with different doses (125, 250 and 500 mg/kg/day) of the aqueous suspension of valerian for 90 days. The following parameters were studied: (1) reproductive organ weight (2) motility and content of sperms (3) spermatozoa morphology (4) cytology of the testis chromosomes (5) study on reproduction (6) biochemical study on proteins, nucleic acids, malonaldehyde (MDA) and non-protein sulfhydryl (NP-SH). The treatment induced significant increase in the weight of caudae epididymis and seminal vesicles and sperm count. There was no effect on sperm motility, morphology of spermatozoa, rate of pregnancy and pre- and post- implantation losses. However, the treatment was found to increase the frequency of chromosomal aberrations. The study on biochemical parameters showed depletion of nucleic acids, NP-SH and increase of MDA, which elucidated the role of free radical species in the induction of chromosomal aberrations. The influence of biochemical changes on induction of chromosomal aberrations and the lack of any effect on spermatogenic and reproductive function is discussed.