Abstract: A magnetic molecularly imprinted polymer with diethylstilbestrol (DESB) as model molecule (MMIP) was prepared and used for separation and pre-enrichment of DESB from environmental water samples and its determination by HPLC. The procedure was given as follows:20 mg of the MMIP is dispersed in 5 mL of methanol to give a suspension which is carried over by wriggling pump into a glass tube with magnets installed on its outer surface. The MMIP particles due to its magnetic property will be pulled and adsorbed on the inner surface of the glass tube, during passing through the tube and then two ends of the tube are plugged with glass wool. Water sample having its acidity adjusted to 7.5, is introduced into the analytical system by passing through the glass tube at a flow-rate of 1.0 mL·min^-1, during which DESB in the sample will be adsorbed on the surface of MMIP adsorbed on the inner surface of the glass tube. Water is used to wash the surface of the MMIP to remove impurities, and then 2 mL of CH₃OH-CH₃COOH (9+1) mixture are used to elute DESB from MMIP. The eluate is used for HPLC determination. It was shown that MMIP had high selectivity for DESB, compounds with similar molecular structure and chemical property did not interfere with the determination of DESB, and that MMIP could be used repeatedly for at least 25 times, showing no significant difference in its adsorption capacity. Value of saturated adsorption of DESB was found to be 93.6 mg·g^-1. Linearity range of DESB found under the conditions described was between 0.20 to 50 μg·L^-1. Detection limit (3S/N) was found 0.06 μg·L^-1. Test for recovery was performed by standard addition method, giving average recoveries in the range of 87.2%-104%. Values of RSDs (n=6) were found in the range of 1.9%-4.6%.