Melinjo (Gnetum gnemon L.) is a native plant in Indonesia. Melinjo peel is generally disposed of, although it contains tannin, flavonoid and saponin, which can be used as antimicrobial compounds. The purpose of this research was to analyze the antimicrobial activity of melinjo peel extract. Maceration method was conducted to extract the melinjo peel, using ethyl acetate as the solvent. The extract at concentration of 4, 8, 12, and 16% (w/v) could inhibit Escherichia coli ATCC 8739, Bacillus cereus ATCC 10876, and Pseudomonas aeruginosa ATCC 9027, but could not inhibit Rhizopus oligosporus ATCC 22959. The extract MIC and MBC value was ranged from 0.50-0.69% and 2.00-2.76%, respectively. Alkaloids, saponin, phenolic, flavonoids and glycosides were found in the extract. The inhibition of selected extract (12%) had a similar level to 1000 ppm Colistin against E. coli and P. aeruginosa. Low pH (pH 4) increased the inhibition of the extract, while neutral pH decreased the inhibition. Heating extract at 65 0 C for 30 minutes increased the inhibition, whereas heating at 75, 85, and 95 0 C decreased the inhibition. The present of salt and sugar at concentration of 1-5% and 10-50%, respectively, increased the inhibition. The extract could damage cell morphology and was confirmed by the presence of ions (Ca 2+ , K + , dan Mg 2+) outside of the cells.