Succinylcholine is commonly administered intravenously, however sometimes it can be administered intramuscularly or sublingually when an intravenous line is not available. We investigated the neuromuscular blocking effect of subcutaneous injection of succinylcholine. The 60 adult patients (ASA 1 or 2) were randomly divided into two groups. After intravenous administration of propofol 3 mg/kg, succinylcholine 1 mg/kg was administered intravenously in one group (IV group, n=10) and subcutaneously in another (SQ group, n=50). Neuromuscular transmission was monitered continuously by the train-of-four (TOF) from response stimulated the ulnar nerve with 2Hz at wrist and the evoked compound action potential of hypothenar muscles was measured with Relaxograph (Datex Co.). We determined the maximum depressed the twitch height (T(TXD)), onset time from injection of succinylcholine to T(MXD), recovery time from T(MXD) to the recovery of 75%, and duration of action from injection of succinylcholine to the recovery of 75%. In the results, T(MXD) of SQ group varied from O% to over 75% compared with 0% in IV group. The onset time of SQ group were more delayed between 7.78±2.80 to 13.08±3.51 minutes compared with 1.08±0.16 minutes in IV group. The recovery time of SQ group were faster between 15.67±10.40 to 2.59±1.75 minutes compared with 18.68±3.68 minutes in IV group. The duration of action of SQ group were not significantly different compared with IV group. And in the SQ group, the lesser depression of twitch height the slower onset time and the faster recovery time was revealed. Conclusively, the subcutaneous administration of succinylcholine 1 mg/kg resulted that the magnitudes of neuromuscular blockade was variable and incomplete, and onset time were slower but recovery were faster than intravenous injection.