OBJECTIVE To compare the effects of fluoroquinolones gatifloxacin and moxifloxacin used for antimicrobial prophylaxis after photorefractive keratectomy (PRK) on epithelial healing. METHODS Forty-four patients randomly received the prophylactic antibiotics gatifloxacin (Gatiflo; 0.3% gatifloxacin ophthalmic solution, Handok, Chungbuk, Korea, no preservative) in 1 eye and moxifloxacin (Vigamox; 0.5% moxifloxacin hydrochloride ophthalmic solution, Alcon Laboratories, Inc, Fort Worth, TX, no preservative) in the fellow eye after PRK. Corneal epithelium was circumferentially removed along a 7-mm zone mark. After PRK, all patients used topical antibiotics 4 times a day until the epithelium healed completely. Starting from postoperative day 1, epithelial healing times and defect sizes were recorded by slit-lamp examination and anterior segment photography. Postoperative pain and discomfort induced by the eyedrops were recorded. Additionally, therapeutic contact lenses were cultured to assess the antibacterial efficacy of fluoroquinolones. RESULTS The mean epithelial healing times after PRK were similar for the 2 groups: 2.97 ± 0.41 days for gatifloxacin and 2.95 ± 0.48 days for moxifloxacin (P = 0.81). There was no statistically significant difference in mean defect size on each postoperative day between the treatment groups. There was no difference in postoperative pain and discomfort. No statistically significant differences were observed between eyes treated with gatifloxacin and moxifloxacin in terms of uncorrected visual acuity or best-corrected visual acuity at 3 months postoperatively. CONCLUSIONS No significant differences were found in the effects of the preservative-free fourth-generation fluoroquinolones gatifloxacin and moxifloxacin on epithelial healing after PRK.