The work attempts to study the surface hydrophobicity (S0) of soy protein isolate（SPI）-guar gum(GG) systems for biomaterial. Effect of four factors on the S0 values of the mixtures were studied. A response surface analysis was carried out using the Box-Behnken Design (BBD)method in order to determine the effects and interactions of pH (6.0, 8.0, 10.0), salt(0.05, 0.15, 0.25M), guar gum(0.10, 0.30, 0.50% w/v) and SPI concentrations (3, 4, 5% w/v) on the S0 values of mixtures. The datas were fitted into second order quadratic model. Salt concentration, pH and SPI concentration, interactions between pH and salt concentration, pH and GG concentration, pH and SPI concentration, GG and SPI concentrations were significant(P<0.05).