BACKGROUND: Crude radix Aconitum kusnezoffii (RAK) has great toxicity. Traditional Chinese medicine practice proved that processing may decrease its toxicity. In our previous study, we had established a new method of RAK processing (Paozhi). However, the mechanism is yet not perfect. OBJECTIVE: To explore the related mechanism of processing through comparing the chemical contents. MATERIALS AND METHODS: A new processing method of RAK named stoving (Hong Zhi) was used. In particular, RAK was stored at 110 degrees C for 8 h, and then high performance liquid chromatography combined with electrospray ionization tandem mass spectrometry (HPLC-ESI-MS(n)) was developed for the detection of the alkaloids of the crude and processed RAK decoction pieces. RESULTS: Thirty components of the crude RAK were discovered, among which, 23 alkaloids were identified. Meanwhile, 23 ingredients were detected in the processed RAK decoction pieces, among which, 20 alkaloids were determined yet. By comparison, eight alkaloids were found in both crude and processed RAK decoction pieces, 15 alkaloids were not found in the crude RAK, however, 10 new constituents yield after processing, which are 10-OH-hypaconine, 10-OH-mesaconine, isomer of bullatine A, 14-benzoyl-10-OH-mesaconine, 14-benzoyl-10-OH-aconine, 14-benzoyl-10-OH-hypaconine, dehydrated aconitine, 14-benzoylaconine, chuanfumine, dehydrated mesaconitine. CONCLUSION: The present study showed that significant change of alkaloids was detected in RAK before and after processing. Among them, the highly toxic diester alkaloids decreased and the less toxic monoester alkaloids increased. Moreover, the concentration changes significantly. HPLC-ESI-MS(n) are Efficient to elaborate the mechanism of reduction of toxicity and enhancement efficacy after processing. SUMMARY: Stoving is a simple and effective method for the processing of radix Aconitum kusnezoffii.In the positive mode, the characteristic fragmentations of Aconitum alkaloids were obtained.The highly toxic alkaloids have decreased, and the new constituents appeared, which has explained successfully the processing mechanism of radix Aconitum kusnezoffii in chemistry.