The solution conformations of three hemorrhagic toxins, designated as AaH I, AaH III and AaH IV, from South Anhui Dienagkistrodon acutus have been studied by CD spectra. The secondary structure of AaH I consisted of 25.8% alpha-helix, 12.7% beta-sheet and 26.8% beta-turns, together with 34.7% random coil. For AaH III, the secondary structure contents were 23.9%, 20.6%, 23.7% and 31.8%, and for AaH IV they were 18.2%, 31.0%, 17.2% and 33.8%, respectively. When pH was lower than 4.0 or higher than 11.0, the alpha-helix decreased but beta-sheet increased, meanwhile, the caseinolytic activities of the three toxins decreased. The activities could be inhibited by EDTA, which indicated that all the three toxins were all metalloproteinases. EDTA, Cu(2+), Zn(2+), Ca(2+) and Mg(2+) could change the secondary structures and play an important role in caseinolytic activities.