Abstract: Macadamia nut polypeptides was prepared by the alkali protease hydrolysis. Eight constituents (MNP-1, MNP-2, MNP-3, MNP-4, MNP-5, MNP-6, MNP-7, MNP-8) were obtained by dialysis technology, its peptides contents, amino acid compositions and antibacterial activities were analyzed. Results showed that the quality proportions and amino acid compositions of different molecular weight Macadamia nut polypeptides were different. Macadamia nut polypeptide MNP-8 had the highest proportions, which was 25.09%, its alanine, valine, leucine, proline and total hydrophobic amino acids related to antimicrobial activity had the hightest proportion, which were 3.38%, 2.42%, 4.67%, 4.39% and 26.92%, respectively.The polypeptide MNP-6 had the higher proportions, which was 18.52%, and was no significant difference with the polypeptide MNP-4 (P>0.05), its lysinerelated to antimicrobial activity had the hightest proportion, which was 6.03%. The antibacterial activities of different molecular weight Macadamia nut polypeptides were also different, which had the better antibacterial activities on the Staphylococcus aureuss, Salmonella typhimurium, Escherichia coli and Pseudomonas aeruginosa, and the worse antibacterial activities on the Candida albicans and Aspergillus niger.Macadamia nut polypeptide MNP-8 had the best antibacterial activities on the Staphylococcus aureuss, Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa and Candida albicans, its diameter of bacteriostatic zones were 15.92, 14.67, 13.70, 16.98, respectively, and 12.47 mm at a concentration of 4 mg/mL, and the MIC were 4.0, 5.0, 4.5, 3.5 and 18.0 mg/mL, respectively.The antibacterial activities of different molecular weight Macadamia nut polypeptides were closely related to their molecular weigh tand amino acid compositions.This study provided the references for the development and utilization of the antibacterial activities of Macadamia nut polypeptides.