Abstract: The binding of qinghaosu (artemisinine) and its derivatives to plasma was studied by equilibrium dialysis. Experimental results showd that there were varied binding of these drugs to plasma protein of human, monkey and mouse. The binding of qinghaosu, o-methyldihydroqinghaosu (MDHQ), dihydroqinghaosu (DHQ) and dihydroqinghaosu hemiester of succinic acid (DHQ-HESA) to plasma protein of human were 64.5±6.8%, 76.9±7.4%, 43.9±6.0% and 59.1±6.6%, respectively.The binding parameters of DHQ-HESA to plasma protein were also determined by two experiments. The parameters obtained were 0.02126×10^-3 and 0.02262×10^-3 M/g for β, —0.9710×10^-3 and —0.5186×10^-3 M/L for K_dp, —0.9781×10^-3 and —1.8174×10^-3 LTM for K,1.6056×10^-3 and 1.7137×10^-3 M/L for NP_t. The number of binding site was about 2.27. The binding of DHQ-HESA was calculated by the parameters, and the values calculated is roughly close to experimental results.