Abstract: OBJECTIVE To establish a LC-MS/MS method for determination of roxithromycin in plasma and to study its bioequivalence. METHODS Clarithromycin was used as internal standard. The method was performed on Alltech Alltima (2.1 mm×100 mm, 3.5 μm) at 30 ℃, and 0.1% formic acid-acetonitrile(45∶55) was used as mobile phase with the flow rate of 0.2 mL·min^-1. Electrospray ionization source was applied and operated in positive ion mode. Selected reaction monitoring(SRM) mode with the transitions of m/z 837.5→679.2 and m/z 748.5→590.2 was used to quantify roxithromycin and clarithromycin, respectively. RESULTS The assay was linear over the range of 0.10-20.00 μg·mL^-1, the limit of detection was 0.01 μg·mL^-1, relative recoveries at three level concentrations ranged from 100.8% to 103.1%, the intra- and inter-day precision(RSD) were below 5.9%. Bioequivalence study showed the test roxithromycin tablets was bioequivalent to the reference tablets. The relative bioavail-ability of the test sample was (100.655±9.552)%(P=0.5%). CONCLUSION The method is simple, rapid, accurate and can be applied to perform the bioequivalence research of roxithromycin tablets.