The discharge capacity, high rate capability and cycle life degradation of the La0.65Nd0.2Pr0.15Ni3.55Co0.75Mn0.4Al0.3 electrode have been investigated. The electrochemical properties of the electrode are significantly improved by partial replacement of La by Nd and Pr. The cycle life degradation of the electrode are examined by using analytical electron microscopy (AEM). Results show that the alloy particles of the negative electrode are gradually oxidized during the charge-discharge process. Microanalysis of the oxidized layer reveals that the oxidation layer is mainly composed of La(OH)(3) and oxides of Nd, Mn and Al. Further observation of the particle morphology after 400 cycles shows that the oxidation layer becomes loose during cycling. The loose oxides cannot protect particles from further electrolytic attack. This may lead to the decrease of the discharge capacity.