Mung bean seed coat (MBSC) is a healthcare product in Asian countries. The aim of this study was to investigate the effect of an MBSC ethanol extract on the bioavailability of cyclosporine A (CsA) in rats. Rats were orally dosed with CsA alone or in combination with MBSC ethanol extracts (500 mg/kg, p.o.). The blood levels of CsA were assayed by liquid chromatography with an electrospray ionization source and tandem mass spectrometry (LC-MS/MS). The everted rat intestinal sac technique was used to determine the influence of MBSC on the absorption of CsA. The results reveal that combined CsA intake with MBSC decreased the C-max, AUC(0-t), t(1/2z) and MRT0-t values of CsA by 24.96%, 47.28%, 34.73% and 23.58%, respectively (P<0.05), and significantly raised the CL/F by 51.97% (P<0.01). The in vitro results demonstrated that significantly less CsA was absorbed (P<0.05). The overall results indicate that after being concomitantly ingested, MBSC reduced the bioavailability of CsA, at least partially, in the absorption phase.