With fresh pig bones' Alcalase hydrolysates as the raw material,ultrafiltration,sephadex G-25 gel permeation chromatography and SP-sephadex C-25 ion exchange chromatography were used to separate and purify the immunomodulating peptides from pig bones. The effects of these peptides on the proliferation of spleen lymphocyte in mouse were determined by MTT. Results showed that the component with molecular weight less than 2ku obtained from hydrolysates through ultrafiltration separation could highly increase the proliferation of spleen lymphocyte in mouse. Then the components with molecular weight less than 2ku were firstly purified by gel permeation chromatography and further purified by ion exchange chromatography. The concentration of component obtained finally was 100μg / m L. It could increase the proliferation of spleen lymphocyte to 114. 30%.