OBJECTIVE: To document the anti-spastic effect and dose-response relationship of gabapentin (GBP) quantitatively using muscle stretch reflex in spinal cord injured rabbits. METHOD: Spinal cords of 25 rabbits were contused by 20 gx20 cm weight drop in the 11th thoracic spine. After 2 weeks, muscle stretch reflex was measured. Triceps surae was dissected and stretched for 5 mm at the rate of 2 mm/sec and the length-tension curve were obtained. The slope in the length-tension curve was defined as stiffness index (SI). After baseline measurement, group I (n=6) received 50 mg/kg GBP IM injection and group II (n=8) received 100 mg/kg GBP IM injection, but control group (n=5) did not. Muscle stretch reflex was measured again after 30 minutes and 60 minutes, and then after sciatic nerve section. Active tension was calculated by subtracting passive tension from total tension. Proportion of SI was calculated by dividing follow-up SI with baseline SI. RESULTS: The proportion of SI of active tension reduced significantly at 30 minutes and 60 minutes compared to baseline (p<0.001, p<0.001). The proportion of SI of active tension in both group I and group II reduced significantly than control group (p=0.041, p<0.001). The proportion of SI of active tension in group II reduced than group I, but it was not statistically significant (p=0.166). CONCLUSION: The GBP reduced significantly muscle stretch reflex in spinal cord injured rabbits and showed dose-response tendency.