Abstract: This study investigated physical and chemical properties of WPG(whole peptidoglycan),which isolated from Lactobacillus paracasei subsp. paracasei X12.And its inhibition activity on the proliferation of HT-29 cells was studied. The molecular weight of WPG was analyze by SDS-PAGE,the amino acid composition was determined by HPLC,the morphology was observed by electron microscopy. Finally,its inhibitory activity against HT-29 cell proliferation was detected. The results showed that the molecular weight of WPG was lower than 14.4 kDa,and there were 15 kinds of protein amino acids,among which the contents of alanine,glutamate,glycine and lysine were higher,and WPG retained the skeleton structure of the whole lactobacillus cell and had the ability to inhibit the proliferation against HT-29 cells. The high-dose peptidoglycan group(160 μg/mL)inhibited the proliferation rate of HT-29 cells was 21.02%.