Objective:The aim of this study to evaluate the effect of muscular electrical stimulation(MES) on muscle weakness in severe sepitc patients requiring mechanical ventilation(MV).Method:Twenty three septic patients requiring MV and having one or more organ dysfunction other than respiratory dysfunction were enrolled within 48 hours from admission to the intensive care unit.Muscular electrical stimulation was administered twice a day on brachial biceps and vastus medialis (quadriceps)of one side of the body until MV withdrawal.Investigators measured arm and thigh circumferences, biceps thickness by ultrasonography, and muscle strength after awakening with Muscle Strength Score System.Result: Six patients died before strength evaluation and were excluded from the analysis.Muscular electrical stimulation was applied for 12±6 days. Biceps（P =0.014） and quadriceps（P =0.007) strengths were significantly higher on the stimulated side at the last day of MES. Circumference of the nonstimulated arm decreased at the last day of MES（P =0.003), whereas no other significant differences in limb circumferences or biceps thickness were observed.Conclusion: Muscular electrical stimulation was associated with an increase in strength of the stimulated muscle in septic patients requiring MV. Muscular electrical stimulation may be useful to prevent muscle weakness in this population.