An ultrasonic extraction technology of preparing catalpol from Radix Rehmanniae was optimized by a uniform experimental design.The optimum conditions for ultrasonic extraction were thus established: 68% (vol) ethanol aqueous solution as extraction solvent

the volume(ml) to mass(g) ratio of extraction solvent to feed of 5∶1

the ultrasonic treatment time of 36 min.The crude catalpol obtained from the optimized ultrasonic extraction technology was further purified by selective adsorption with macroporous resin.The adsorption capacities and desorption yields of ten kinds of macroporous resins for catalpol were investigated.The results showed that H103 resin possessed the best performance.The properties of dynamic adsorption and desorption of H103 resin for catalpol were subsequently investigated on adsorption column.The optimum conditions for adsorption and desorption were determined.The concentration of catalpol in the loaded sample solution was 6.15 mg·ml-1

the flow rate was 1.0 ml·min-1

the volumetric percentage of ethanol in the eluting solvent was 75%，the elution flow rate was 0.5 ml·min-1 and the elution volume was 3.33 BV(bed volume).Under the above conditions

the purity of catalpol product eluted from the column packed with H103 resin reached 62.39% while that of the crude catalpol was only 10.01%.