The paper studied antibacterial effects in vitro of gelatin, nano-SiO2 and gelatin/nano-SiO2 composite membranes on 6 kinds of bacteria. The results indicated that gelatin had no antibacterial effect; nano-SiO2 had antibacterial effect; 11 out of 20 kinds of gelatin/nano-SiO2 composite membranes had strong antibacterial effects. Their minimal inhibitory concentrations (MICs) were also tested using the method of plate dilution, and the results indicated that they had different MICs because of different membranous formula and different bacteria. There were differences of MICs for different bacteria. For Bacillus cereu, MIC was 256.0 mg/mL; but for other bacteria, MICs were mainly 64.0 mg/mL-128.0 mg/mL.