The history of muscle relaxant is fascinating, and their use in clinical anesthesia has been accepted. Depolarizing muscle relaxant may produce prolonged apnes with dual block and has no antidote. But non-depolarizing muscle relaxant has an antidots so whenever it is able to get reversal of muscle relaxation. Obviously, return of normal muscle function following muscle relaxant administration is of prime importance to the restoration of adequate spontaneous ventilation because it is clinically very important. By the way, there is no report on the effect of neuromuscular blocker with neostigmine pretreatment. The experiment was performed on forty rabbits weighing 1.8 to 2.4 kg and these were divided into two groups: eighteen rabbits for the control and twenty two rabbits for the study group. All animals were intubated through a tracheostomy under the general anesthesia with urethane and thiopental. Respiration was controlled by shinano animal respirator. The body temperature was kept at 35 to 36 ℃ with a thermo-blanket. The common peroneal nerve and anterior tibial muscle was exposed and the peripheral nerve simulator was applied to the nerve muscle preparation. The twitch height of the muscle contraction was recorded on a biophysiograph through the force displacement transducer. The common peroneal nerve was stimulated supramaximally using a single twitch, square wave of 0.2msec duration at a frequency of 1 Hz. The degree of neuromuscular block and recovery following intravenous injection of succinylcholine 0.2mg/kg and pancuronium 0.02mg/kg were measured in the control group. And in the study group, succinylcholine 0.2mg/kg and pancuronium 0.02mg/kg were administered intravenously five minutes after the intravenous neostigmine then neuromuscular block and recovery were measured. The change of the twitch height on the muscle contraction and the time of spontaneous recovery in the study group were compared with those of the control group. The results were as follows: 1) Neostigmine pretreated succinylcholine effect was markedly prolonged muscle relaxation(about 7 times) and twitch height was diminished to 61.4% of the control level. 2) Neostigmine pretreated pancuronium effect was not afected significantly compare to the control group.