Proteins and polysaccharides are two biopolymers that widely used as functional ingredients in various food formulations. These two components can determine the stability, structure, viscoelastic and texture properties of numerous food systems. Various physical, chemical and enzymatic techniques have been developed in order to improve the functional properties of proteins. Proteins Modification by the enzymes attracts more attention of researchers and industries than the other kind of modification because the enzymatic modification has specific activities, the mild reaction and does not form unwanted and toxic compounds. The aim of this research was to study the application of microbial Transglutaminase (mTGase) as the biocatalyst to modify Soy Protein Isolate (SPI) by conjugate to Acacia gum and evaluate functional properties of the modified products. The conjugates were prepared at biopolymers concentration of 3% and 6% in the reaction environment during 0, 30, 60, 120 and 240 minutes. The result of the free amino groups assay indicated that the higher the total biopolymers concentration the higher intensity of reaction was occurring. The result of Fourier transform infrared spectroscopy (FTIR) showed that the reaction has an effect on the secondary structure of protein and even this reaction has an effect on the hydrogen bonds and hydrophobic interactions due to TGase activity. Increasing protein molecular weight was determined by gel electrophoresis. The results of gel electrophorese indicated that the basic glycinin fraction had fewer tendencies to participate in a reaction catalyzed by TGase than other parts of SPI. The cross linking reaction of Gum Arabic and SPI by Transglutaminase and formation of the higher molecular weight products were confirmed by gel permeation chromatography analysis. The turbidity of sample solutions showed a significant increase with the increase of reaction time. Moreover, the samples obtained from higher concentrations of biopolymers made more turbid solution. The results of functional properties demonstrated a decrease in solubility, emulsifying activity and stability index of samples by increasing the reaction time and concentration of reactant. But viscosity of samples solutions and their emulsions and their foam stability were increased. Significant differences in foaming ability of samples were not observed. Keywords: Cross-linking, Functional properties, Transglutaminase, Soy Protein Isolate, Acacia Gum