The black cumin or Nigella sativa L. seeds have many acclaimed medicinal properties. Pharmacological studies have been conducted on the aqueous and methanol extracts of N. sativa L. seeds to evaluate their effects on the central nervous system. In the present study, N. sativa oil was used to study its effect on anxiety in rats. Open field and elevated plus maze models were selected for the evaluation of anxiolytic effect of drug. After four weeks of daily administration of drug, the rats exhibited an increase in open field activity. The drug also produced anti-anxiety effect in rats when tested in elevated plus maze. Concentrations of 5-HT, 5-HIAA in brain and concentrations of plasma and brain tryptophan determined by HPLC-EC detector. Result shows that oral administration of N. sativa oil increased brain levels of 5-HT but the levels of brain 5-HIAA decreased significantly. Brain and plasma levels of tryptophan also increased significantly following oral repeated administration of N. sitiva oil. Based on this, it may be suggested that N. sativa oil is a useful choice for the treatment of anxiety.