Purpose: The aim of this study is to estimate one mouthful volume in a single swallow and average volume per swallow (AVS) in multiple swallows in the situation of toxic liquid poisoning. Methods: Thirty five men and 35 women were included in this study. Each subject was asked to drink one swallow and three consecutive swallows from bottle containing water and a bottle containing saline separately. We calculated one mouthful volume in a single swallow and AVS in three swallows. One mouthful volume and AVS were compared according to sex and content, respectively. One mouthful volume of water and saline was then compared with AVS of each. Results: Sixty seven adults(34 men; $26.9{pm}3.2$ years, 33 women; $25.6{pm}2.4$ years) completed the study. Men had larger one mouthful volume of water($49.1{pm}19.9$ ml vs $39.7{pm}10.2$ ml, p=0.02) and saline($20.7{pm}10.9$ ml vs $14.0{pm}4.6$ ml, p=0.004) and AVS of water($28.5{pm}11.9$ ml vs $21.5{pm}5.9$ ml, p=0.004) and saline($11.9{pm}6.3$ ml vs $7.9{pm}2.0$ ml, p=0.001) than women. One mouthful volume and AVS of saline swallow were lower than those of water swallow. AVS of three consecutive swallows was lower than one mouthful volume in water and saline swallow. Conclusion: We suggest that one mouthful volume in a single swallow is 21 ml in men and 14 ml in women and AVS in multiple swallows is 12 ml in men and 8 ml in women. AVS in multiple swallows is two-threefold lower than reference values(20~30 ml) commonly used in poisoning study.