Abstract: The arsenic species in rat plasma were studied after oral administration of realgar and Niu Huang Jie Du Pian (NHJDP) and the possible compatible effects of realgar was evaluated by comparing the pharmacokinetics of arsenic species after administration of realgar and NHJDP. The separation of the arsenicals was performed by a high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) technique. Dimethylarsinic acid (DMA) was found to be the main species in rats' plasma after dosing. No traces of arseniteAs(Ⅲ), monomethylarsonic acid (MMA) or arsenateAs(V) were detected at any sampling time points. Compared with realgar administration alone, dose-normalized peak concentration (C_max) and AUC_0-t of DMA were significantly decreased by NHJDP administration, while the t_max was significantly delayed with the clearance and apparent volume of distribution significantly increased, indicating that the pharmacokinetics of As from realgar was affected by other ingredients in the compound prescription of NHJDP.