Drug is a chemical material used to prevent, cure, and diagnose a disease. Nethisterone is adrug that consumed to prevent pregnancy, but it can produce androgenic side effects such as hirsutism, acne and voice changes of slight vehemence in some women at average and high dosages. Since no study has been done onside effect of Nethisterone tablet on anxiety, therefore, the aim of the study was determination of side effect of the tableton anxiety in female mice. As a screen test to discover side effect of the drug on anxiety, Light/dark Transition test was employed. The light/dark transition defecation test was done in a 21x42x25cm cage partitioned by 2 same sized chambers with a door. One chamber was illuminated brightly and the other was dark. In the test, the time spent and defecation in during test in both chambers are good indexes of anxiety-like behavior. The results indicates that mice in group 2 (In the group, mice received Nethisterone) to group 1 (Control group=in the group, mice received saline) tend to stay in the light chamber and defecation in both chamber. Thus, the present research demonstrates the effect of Nethisterone in increasing anxiety. It is recommended that women do not use this drug in averages and high doses.