BACKGROUND: The cuff inflation of laryngeal mask airway (LMA) with excessive volume of air may injure soft tissue and nerves around hypopharynx because of high cuff pressure. But it is not well known about adequate cuff volume of LMA. The cuff inflation of LMA in hypopharynx accomodate pharynx, so various injection volume may differ in sealing effect. This may influence ventilation. This study was proposed to investigate the effect of cuff volume on cuff pressure and ventilation when LMA inserted. METHODS: Fifteen male patients were inserted with #4 LMA, fifteen female patients were inserted #3 LMA. For male patients, 10, 20, 30 and 40 ml of air were injected into cuff of LMA and 10, 15, 20 and 25 ml for female patients. Cuff pressure, minute ventilation and airway pressure were randomly measured. RESULTS: Volume of injected into cuff and cuff pressure of LMA were closly related. But minute ventilation and airway pressure were not related with injected air volume of LMA. CONCLUSION: Excessive volume of air injected to LMA cuff was not beneficial to ventilation. So minimal sealing cuff volume under maximal recommended volume of LMA may reduce the incidence of complications associated with high cuff pressure.