In this study the relationship between degree of spasticity and strength of knee extensor and ankle plantar flexor muscles of post stroke hemiparetic patients has been investigated.The participants of this study were 40 stroke patients whose elapsed time of stroke onset was at least 3 months. Their age averaged 59 years. Spasticity was measured with the Modified Ashworth Scale. Isokinetic muscle strength was measured with an isokinetic dynamometer. Two methods of torque normalization - subtractive and weight based normalization - were used for comparing torques among participants.Kendall's tau-b coefficient was calculated for investigating this relationship. This coefficient was not significant for the relationship between weight based normalized data and modified Ashworth scale (MAS) in any of each muscle groups (α = 0.05). This coefficient was significant for the relationship between the subtractive normalization method and MAS in knee extensors (P = 0.005, α = 0.01) and ankle plantar flexors (P = 0.002, α = 0.01).This study suggests a negative relationship between spasticity and muscle strength and provided evidence that spastic muscles are weaker.