Nigella sativa seeds (blackseed) have been used in traditional medicine for the treatment of a variety of diseases including diarrhea and asthma, and have been shown to have various useful pharmacological effects. In this study, acute and subacute toxicity of the aqueous, methanol and chloroform extracts of the seeds have been investigated. To determine their LD50, the aqueous, methanol and chloroform extracts were administered orally, in 4 different doses, 6, 9, 14 and 21 g/kg. Mortality rate and weight changes have also been measured in all groups for 3 and 7 days, respectively. No mortality has been observed in all groups and with all doses. Methanol extracts in all doses and chloroform extract in the dose of 21 g/kg significantly decreased animals weight. Hepatic toxicity of the extracts was also investigated in the dose of 6 g/kg/day orally for 14 consecutive days by measuring ALP, SGOT and SGPT activity in blood and hepatic histological study. Degenerative changes in hepatic cells have been observed only with aqueous extract of the seeds. In conclusion, Nigella sativa extracts are relatively nontoxic in the acute toxicity test, but the possibility of hepatic damage with its aqueous extract should be considered.