To identify Kraft liquor effects on spermatogenesis and sperm motility of Caspian kutums by using in vitro culture, the fish testis was incubated with 5, 10 and 15 % (V/V) of liquor for 3 and 6 days. The percentage of motile spermatozoa and its total duration were also measured. Adverse effects on testicular cells were more apparent with the increase of liquor concentrations. The mean size of spermatogonia and spermatocytes decreased significantly (p < 0.001) in dose-dependent manner compared to controls. With the increase of concentration, the number of spermatocytes and spermatids decreased (p < 0.001) but the number of spermatogonia, increased (p < 0.05). The increase of liquor concentration showed a significantly decrease of percentage of motile spermatozoa and total duration of spermatozoa (p < 0.05) but there was no significant difference in most treatments (p>0.05). This study showed the detrimental effects of low levels of kraft liquor on testicular development and sperm quality in the kutums.