AIM: To observe the efficacy of 5g/L levofloxacin eye drops on severe bacterial keratitis and severe bacterial conjunctivitis. METHODS: Subjects diagnosed as severe bacterial keratitis or severe bacterial conjunctivitis in out-patient department were treated with 5g/L levofloxacin eye drops, and the severe patients were treated with combination therapy. Visual acuity, ocular manifestation, ulcer depth, tissue necrosis and hypopyon were recorded before and after treatment, and pathogenic tests were carried out. RESULTS: In 15 cases(18 eyes) with severe bacterial keratitis, the mean pre-treated visual acuity was 0.1±013, and positive ratio of pre-treated germiculture was 83% (12 cases, 15 eyes). The main pathogens included Nocardia, Acinetobacter lwoffii, burkholderia gladioli, Mycobacterium chelonei,Streptococcus,and Staphylococcus, in which bacillus occupied a percentage of 73%(11/15). Both symptoms and signs started to ameliorate in day 3 after treatment (P<0.01). A bacterial elimination rate post-treatment of 93% was observed, with the overall effective rate of 94%. Mean treatment duration was 21±482 days, and the mean visual acuity of post-treatment was 0.5±0.26. In 21 cases(32 eyes) with severe bacterial conjunctivitis including, the mean visual acuity of pre-treatment was 0.6±0.31. The positive germiculture ratio was observed to be 69% (15 patients and 22 eyes) before treatment, with staphylococcus (68%,15/22),α-hemolytic streptococcusand and pseudomonas as the main pathogens. Amelioration was noticed in both symptoms and signs from day 2 after treatment (P<001). The bacterial elimination rate of post-treatment was 91%, overall effective rate is 97%, mean treatment duration was 15±3.23 days, and mean post-treated visual acuity is 0.7±029. Correlation was found in either group between treatment duration and bacterial strains (P<0.05). CONCLUSION: The vital pathogens in severe bacterial keratitis was bacillus, followed by Staphylococcus and Streptococcus. The mean treatment duration was 3 weeks. The vital pathogens in severe bacterial conjunctivitis was Staphylococcus, followed by Streptococcus and Pseudomonas bacillus, and a mean of 2-week treatment was recorded. Visual improvement was found in either group without deterioration in any cases. 5g/L levofloxacin may effectively treat severe bacterial keratitis and severe bacterial conjunctivitis, and in severe cases a proper combination is recommended. No side effect was found in our study.