Abstract: The optimum processing conditions of enzyme- assisted extraction of polysaccharides from Hylocereus undatus were studied by single factor experiments and response surface. The antibacterial activity of Hylocereus undatus polysaccharose was evaluated. Results showed that the optimum process parameters were cellulose enzyme,the dosage of Enzyme was 0.1200 g,liquid- solid ratio was 20∶1,extraction at 65 ℃ for 50 min.The yield of Hylocereus undatus polysaccharides under the optimized conditions was 16.64%.Antibacterial results showed that the polysaccharide of Hylocereus undatus had good antibacterial activity,and best against Escherichia coli,followed by Staphylococcus aureus,Saccharomyces carlsbergensis,Aspergillus niger,antibacterial activity against Bacillus subtilis had the lowest activity. The minimal inhibitory concentrations( MIC) varied from 5 mg / m L to30 mg / m L.