Abstract: The separation of rare earth metal ions by capillary ion electrophoresis in the presence of imidazole as UV-absorbing background electrolyte and α-hydroxyisobutyric acid as the complexing agent with indirect UV absorbance was investigated. Several experimental condition influenced on separation was atudied. Using 0.02mol/L imidazole containing 8×10^-3/L α-hydroxyisobutyric acid(pH3.4) as a carrier electrolytr, the fourteen rare earth metal iorns were separated within 10min under a positive voltage of 10.0kV.The content of La、Ce、Pr、Nd、Sm in rare earth chloride sample from Gansu Rare Earth Company was determined successfully with this method.