An improved HPLC-electrochemical detection (ED) method is described for the analysis of hydroxyurea (HU) in human plasma. After extraction process, HU was determined on a C18 column (250mmx4mm) by the mobile phase (25mM sodium acetate-acetonitrile, 97.5:2.5; pH 6.5). The regression equations were linear (r>0.9990). The precision and accuracy of intra- and inter-batches were all below 5% for relative standard deviation (R.S.D.) and relative error (R.E.). Based on 20μl of plasma, the limit of detection was 0.3μM for HU (S/N=3, injection 10μl). This method was applied for the HU drug monitoring of patients with myelofibrosis or polycythemia vera.