An efficient and sensitive ultra-performance chromatography–tandem mass spectrometry method to simultaneously determinate and quantify mosapride (M) and its des-p-fluorobenzyl (M1) and 4′-N-oxide (M2) metabolites using carbamazepine as the internal standard (IS) in rat plasma has been developed and validated. Analytes were extracted from aliquots of plasma with ethyl acetate after alkalization using saturated sodium carbonate solution. The chromatographic separation was conducted on a BEH C18 column (100mm×2.1mm, 1.7μm) with the gradient elution using a mobile phase of acetonitrile – 0.2% formic acid in water at a flow rate of 0.25mL/min for 4min. The tandem mass spectrometric detection was conducted using multiple reaction monitoring (MRM) by the positive electrospray ionization (ESI). The ion transitions monitored were m/z 422→198 for mosapride, m/z 314→198 for M1, m/z 438→109 for M2 and m/z 237→194 for IS. The linear ranges of the calibration curves were 1.0–2000ng/mL for M, 0.75–1875ng/mL for M1 and 0.4–40ng/mL for M2. And the corresponding lower limits of quantitation (LLOQ) of the method were 1.0, 0.75, 0.4ng/mL for M, M1 and M2, respectively. The intra- and inter-day precision for all analytes were less than 8.1% and 11.6%, respectively. The inter-assay mean accuracy was between −6.4% and 8.1%. No relevant cross-talk and matrix effect were observed. There were significant differences between male and female rats for M, M1 and M2. Display omitted •A UPLC–MS/MS method for analysis of mosapride and its two metabolites was developed.•The method was successfully applied to a pharmacokinetic study in rats.•Lower limit of quantification of 1.0, 0.75, 0.4ng/mL were achieved.