Parkinson’s disease (PD) is a degenerative disorder of the central nervous system. Early in the course of the disease, the most obvious symptoms are movement-related, including: shaking, rigidity, slowness of movement and difficulty with walking and gait. Rigidity is stiffness and resistance to limb movement caused by increased muscle tone, an excessive and continuous contraction of muscles. Effects of different herbal preparations have been evaluated on muscle rigidity so far and some of them are approved in clinic. In the present research, the effects of Nigella sativa hydroalcoholic seed extract on muscle stiffness in perphenazine-induced muscle rigidity were evaluated in adult male mice. In this experimental study, L-dopa 10 mg/kg, Nigella sativa hydroalcoholic seed extract at 50, 100, and 200 mg/kg were administered orally to male Balb/c mice for 12 days. Control group only received water. Muscle rigidity scores were then measured and compared. The muscle rigidity score in group receiving extract at 50 mg/kg had no significant difference with control group but at 100 mg/kg it had been significantly improved starting at the 40th minute. The extract at 200 mg/kg had significant difference in all times measured in comparison with control group that also showed lower scores compared to L-dopa treated group. According to the obtained results in this study, it can be concluded that Nigella sativa hydroalcoholic extract has good effects on muscle rigidity in dose-dependent pattern.