Background: Aceclofenac is a phenylacetic acid derivative with analgesic and anti-inflammatory properties and an improved gastrointestinal tolerance compared with other NSAIDs, such as diclofenac. Objective: This study was conducted to compare the bioavailability of 2 branded formulations of aceclofenac 100 mg (test and reference) marketed in Korea. Methods: This single-dose, randomized, open-label, 2-period crossover study in healthy Korean adult volunteers was conducted at Hanyang University Medical Center (Seoul, Republic of Korea). Subjects received 1 tablet of each aceclofenac 100-mg formulation. Study drugs were administered with 240 mL of water after a 10-hour overnight fast on each of 2 treatment days separated by a 1-week washout period. After study drug administration, serial blood samples were collected over a period of 12 hours. Plasma was analyzed for aceclofenac concentration using a validated high-performance liquid chromatography method with visible detection in the range of 0.1 to 20 μg/mL, with a lower limit of quantitation of 0.1 μg/mL. Several pharmacokinetic (PK) parameters, including Cmax, Tmax, t1/2, AUC0-t, AUC0-∞, and ke, were determined from the plasma concentrations of the 2 aceclofenac formulations. Cmax, AUC0-t, and AUC0-∞ were used to test for bioequivalence after log-transformation of plasma data. The predetermined, regulatory range of 90% CI for bioequivalence was 0.80 to 1.25. Results: A total of 24 subjects were enrolled (20 men, 4 women; mean [SD] age, 23.5 [1.4] years; mean [SD] weight, 68.1 [11.5] kg). No significant differences were found based on analysis of variance, with mean values and 90% CIs of test/reference ratios for these parameters as follows: Cmax, 10.57 versus 9.79 μg/mL (0.961-1.225); AUC0-t, 19.95 versus 19.93 μg · h/mL (0.937-1.037); and AUC0-∞, 20.75 versus 20.48 μg · h/mL (0.949-1.049). Conclusion: In these healthy Korean volunteers, results from the PK analysis suggested that the test and reference formulations of aceclofenac 100-mg tablets were bioequivalent, based on the regulatory definition.