A simple and sensitive high-performance liquid chromatographic (HPLC) method was developed for quantification of aceclofenac in rat plasma. Ibuprofen was used as an internal standard (IS). The present method used protein precipitation for extraction of aceclofenac from rat plasma. Separation was carried out on reversed-phase C18 column (250 mm × 4.6 mm, 5 μ) and the column effluent was monitored by UV detector at 282 nm. The mobile phase used was methanol-triethylamine (pH 7.0; 0.3% v/v in Milli-Q water) (60:40%, v/v) at a flow rate of 1.0 mL min-1. This method was linear over the range of 50.0-3500.0 ng mL-1 with regression coefficient greater than 0.99. The mean recovery of aceclofenac and IS were 84.62 ± 3.23 and 89.19 ± 1.57%, respectively and the method was found to be precise, accurate, and specific during the study. The method was successfully applied for pharmacokinetic study of aceclofenac in rats. © 2006 Elsevier B.V. All rights reserved.