The antimicrobial activity of lysosomes, a cell organelle, against a range of test microorganisms was examined in this study. The lysosomes isolated from Saccharomyces cerevisiae showed antimicrobial activity to Escherichia coli that positively correlated with the pH of the phosphate buffer as a dissolving solvent. The lysosomes from S. cerevisiae exhibited optimal activity at a concentration of 40%, at pH 4.0 of phosphate buffer, and at broad range temperature, except of over 50A degrees C. It was also found that the lysosomes have antimicrobial activity against seven different microorganisms including E. coli. In addition, S. cerevisiae were exposed by a treatment with H2O2 and lysosomes were isolated from H2O2 exposed S. cerevisiae. We found that fluorescent intensities of each isolated lysosomes were increased depending on the increment of treated H2O2 concentration, and the lysosomes from 20 mM H2O2 treated S. cerevisiae showed higher antimicrobial activity than those from normal S. cerevisiae. Therefore, it suggests that lysosomes isolated from S. cerevisiae can be used as an antimicrobial agent. In addition, lysosomes activated by H2O2 enhanced its antimicrobial activity.