In order to study the flavor characteristics of peptides with different molecular weights via Maillard reaction, the protein hydrolysates were obtained by enzymatic hydrolysis using soy protein and chicken as raw materials. Then the enzymatic hydrolysates were separated by ultrafiltration to obtain peptides with different molecular weights, less than 1000Da, 1000~5000Da and greater than 5000Da. In addition, the complex amino acids were obtained by complete acid hydrolysis of enzymatical hydrolysates of soybean and chicken. A certain amount of xylose was added in peptides and amino acids to build a Maillard reaction model. The sensory properties of Maillard reaction products were evaluated. Then the volatile and nonvolatile compounds were analyzed by gas chromatography-mass spectrometry and high-performance liquid chromatography. The results showed that in the Maillard product of enzymatical hydrolysates of two different protein sources, a total of 69 kinds of volatile compounds were identified, among which the contents of pyrazine, furanthiol and other meat flavor compounds were the highest. Statistical analysis showed that there were significant differences in volatile compounds of peptides with different molecular weights and free amino acids. The formation of pyrazine compounds was promoted by peptides less than 1000Da during the Maillard reaction, such as pyrazine, 5-methyl-2-ethylpyrazine, 2,5-methyl-3-ethylpyrazine, trimethylpyrazine, 2-acetylpyrrole, etc. Compared with peptides, free amino acids favored the formation of sulfur-containing compounds such as furanthiols and thiophenes. Only 29 volatile compounds had relative odorant activity values (rOAV) greater than 1. Partial least squares regression (PLSR) was used to investigate correlations between key odor compounds and sensory evaluations. Peptides less than 1000Da were found to be closely related to the basic meaty and kokumi, while peptides greater than 5000Da were closely related to bitter and burnt flavor. After Maillard reaction, the amount of peptides greater than 5000Da was significantly reduced. Degradation of peptides of 1000-5000Da could replenish the consumed free amino acids. The peptides less than 1000Da were prone to cross-link and polymerization and thus increased the content. The products had a significantly enhanced effect on the flavor, and could contribute well to the basic meaty, umami and kokumi. It was hoped that this study could provide theoretical support and guidance for the application of proteolysates to produce Maillard reaction products.