This study was attempted to investigate the effects of enzymatic modification of milk protein with protease on functional properties. The selected functional properties were solubility, emulsifying activity (EA), emulsion stability(ES), foam expansion(FE), and foam stability(FS). These properties were measured from pH 3.0 to pH 8.0. The proteases used in this study were iaolated from Meju(fermemted soybean) and had specific activity of 250 units/㎎ protein at pH 7.0, 1600 units of protease was used for 1gr. of skim milk protein. Skim milk showed 30.5% degree of hydrolysis for 1hr. and 36.4% degree of hydrolysis for 3.5hrs. of protease treatment at pH 7.0. Solubility of native skim milk, control, 1hr. and 3.5hrs. groups were 3.37, 3.64, 10.21, 14.34% at pH 4.0 respcetively. The emulsifying activity of native skim milk, control, 1hr. and 3.5hrs. groups were 38.8, 42.0, 43.0, 46.7% at pH 4.0, respectively. Enzymatic modification resulted in the increase of solubility and emulsifying activity at pH 4.0. However at pH 5.0 emulsifying activity of 1hr. and 3.5hr. group were lower than native skim milk and control groups. 1hr. protease treatment was found to be most effective way of increasing foam expansion at pH 4.0 to 6.0. It was supported that, protease treated skim milk can be used to improve solubility, emulsifying activity, foam expansion at acid pH.