Abstract: An HPLC method foY the determination of in vivo release of norethindrone-α,β-poly(3-hydroxypropyl)-DL-asparamide(NET- PHPA )conjugate was established using column switch-ing technique. The sample prepurification could be omitted. It was extracted by a precolumn(ODS,9～11μm)and the analytical column was packed with ODS(15 cm×4 mm ID, Shimpac CLC).Themobile phases were water and methanol一water(7:3) respectively. The experiment showed that therecovery from serum was 82.6%,the RSD within day was l.3～1.8%and that in day一to一daywas 0.7～5.6%(n=4).