AIM: To study the efficacy of 1,5,25g/L of three different concentrations of povidone-iodine in reducing the rate of positive conjunctival bacteria cultures,and to observe their adverse effects.METHODS: This was a comparative study.205 patients(205 eyes) who underwent cataract phacoemulsification cataract surgery were randomly divided into three groups.At preoperative 1 day,all patients received 3g/L ofloxacin eye drops 3 times.Approximately 5-10 minutes before surgery,the conjunctival sac was irrigated with 20-30mL 1,5,25g/L povidone-iodine,correspondingly.Conjunctival cultures were obtained at the following time points: before receiving any topical medications;after application of 1-day topical 3g/L ofloxacin,before irrigating the conjunctival sac;immediately before surgery,approximately 5-10 minutes after conjunctival sac irrigation and at the end of the surgery.The rate of positive conjunctival cultures among each group was compared and significance of the difference was tested with the Pearson Chi-square test.And adverse effects of the povidone-iodine were observed.RESULTS: The rate of positive conjunctival cultures before the conjunctival irrigation in the 1g/L povidone-iodine group,5g/L povidone-iodine group and 25g/L povidone-iodine group was 63.0%,61.4% and 59.6%,respectively;after surgery was 12.3%,11.4% and 12.9%.The differences of positive rates before the conjunctival irrigation and after the surgery in the corresponding group were statistically significant(χ2=54.88;57.61;40.47,all P=0).Both before the conjunctival irrigation and after surgery,the difference of positive rate among these three groups were not statistically significant(χ2=0.15,P=0.92;χ2=0.06,P=0.96).62 cases of the 25g/L povidone-iodine group had 4 cases with conjunctival congestion and mild corneal edema,accounting for 6%,no other adverse reactions,the other two groups were found no significant adverse reactions,the difference among the three groups was statistically significant(χ2=9.4,P=0.009).CONCLUSION: Three concentrations of povidone-iodine of 1,5,25g/L have similar effects on the reduction of the bacteria in conjunctival sac,but low concentrations of povidone-iodine of 1g/L and 5g/L are more secure.