Abstract: OBJECTIVE To explore the reasonable dosage of the antimicrobial agent in Latanoprost eye drops. METHODS According to characteristic of drug ingredients, choose appropriate antimicrobial agents, according to Chinese Pharmacopoeia 2015 Version bacteriostat effect test, the test strains of Staphyococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candia albicans and Aspergillus niger, combination of preservation benzalkonium chloride and ethylparaben according to different join the amount and configuration for antibacterial effect of food inspection. RESULTS A, B, C group combined with the application of preservatives can achieve the prescribed antibacterial effect. 0.03% benzalkonium had a good inhibitory effect on growth of ammonium chloride and 0.015% ethylparaben preservative combined application of the above 5 kinds of test bacteria, and was the lowest effective concentration. CONCLUSION The determination of 0.04% benzalkonium chloride and 0.03% phenoxy ethanol as a bacterciostatic agent of Latanoprost eye drops.