For biometric study on the width of mouth in the vietnamese, the author measured the transversal width of mouth and longitudinal width of mouth in 1021 healthy cases. of the total cases, 506 were male and 506 female and ages ranged from 1 to 30 over years old. The following result was obtained: 1) In adult, transverasal width of mouth was 49.23±0.24 in male, 49.67±0.31 in female and 39.14±0.22 in male, 41.01±0.23 in female of children. 2) In adult, longitudinal width of mouth was 52.82±0.24 in male, 51.89±0.28 in female and 40.92±0.37 in male, 42.97±0.29 in female of children.