Objective To evaluate the efficacy of topical and systemic antimicrobial application on reducing con-junctival sac bacterial flora. Methods 82 cataract patients (164 eyes)were randomly selected for studying,non-surgical eye of the same patient was as control eye. Surgical eyes received 3-day preoperative 0.5% levofloxacin eye drops,all patients received systemic antimicrobial agents 30 minutes before surgery. Specimens from conjunctival sac were collected at the following time points:admission (T0);3 days after receiving 0.5% levofloxacin eye drops before surgery (T1);30 minutes after all patients received systemic antimicrobial agents (T2),all specimens were performed bacterial culture. Results The percentage of positive cultures for surgical and control eyes was 42.68%(35/82)and 43.90% (36/82)at T0,0 (0/82)and 8.54% (7/82)at T1,0(0/82)and 0 (0/82)at T2,respectively. Conclusion Topical and systemic antimicrobial application can reduce conjunctival sac bacteria. Because of the side effects of systemic antimicrobial agents,preoperative routine systemic antimicrobial use is not suggested.