Isokinetic test of muscle strength was performed on 20 patients operated laminectomy & discectomy. Peak torque of ankle dorsi flexors & plantar flexors at the angular velocity of $30^{circ}$/sec and average power and total work of ankle dorsi flexors & plantar flexors at the angular velocity $90^{circ}$/sec were measured and analyzed. The result were as follows: 1. Peak torque of non - dominant dorsi flexors at $30^{circ}$/sec showed no significant difference statistically, but dominant dorsi flexors at $30^{circ}$/sec showed significant difference statistically(p<0.05). 2. Peak torque of dominant & non - dominant plantar flexors at $30^{circ}$/sec showed significant difference statistically(p<0.05). 3. Average power of dominant & non - dominant dorsi flexors at $90^{circ}$/sec showed no significant difference statistically. 4. Average power of dominant & non - dominant plantar flexors at $90^{circ}$/sec showed significant difference statistically (p<0.05). 5. Total work of dominant & non - dominant dorsi flexors at $90^{circ}$/sec showed no significant difference statistically. 6. Total work of dominant & non - dominant plantar flexors at $90^{circ}$/sec showed significant difference statistically(p<0.05).