Capillary Electrochromatography (CEC) driven by electroosmotic flow is a new technique using fused silica capillaries packed with HPLC-type stationary phase. The analytes are separated by normal chromatographic partition between a mobile phase and a stationary phase. By using electroosmotic flow driving mobile phase, CEC promises theoretical plate efficiencies for HPLC. In this paper, some separating characteristics in capillary electrochromatography were studied by carrying out the separation of some neutral compounds on capillary column with 75microm i.d. x 30cm/37cm packed with ODS particles (3microm). The mobile phase was acetonitrile and water, which contains certain concentration of electrolyte. Samples were injected electrokinetically into the separating column. On-line UV detector was used. The Joule heating effect in packed CEC was lower than that in CZE, and a good linear relationship between the elecrtoosmotic flow (EOF) velocity and applied voltage was obtained as shown in Fig. 1. The influence of electrolyte and acetonitrile concentrations on the electroosmotic flow was studied, as shown in Fig. 2 and 5. The EOF was monitored by using thiourea as a marker. The EOF will decrease when the electrolyte concentration increases. The higher the acetonitrile concentration was, the lower the EOF was. The effect of linear velocity on column efficiencies was also investigated. The column effeciencies less than 2. 0 reduced plate height were obtained. The highest efficiency obtained in this work was 236000 plate per meter for a retained solute, benzene. It was found that the concentrations of acetonitrile and electrolyte were important experimental variables in performance of capillary electrochromatography.