ObjectiveTo evaluate the efficacy of topical and systemic antimicrobial application on reducing conjunctival sac bacterial flora. Methods82 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. ResultsThe 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. ConclusionTopical 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.