LiNi1/3Mn1/3Co1/3O2 compound was successfully synthesized by the co-precipitation method. The effect of H2O on LiNi1/3Mn1/3Co1/3O2 in humid atmosphere was investigated by structural, magnetic and electrochemical analysis, and Raman spectroscopy. The consequence is that immersion of LiNi1/3Mn1/3Co1/3O2 to H2O and exposure of LiNi1/3Mn1/3Co1/3O2 to humid atmosphere (ambient atmosphere, 20°C, 50% relative humidity) led to a rapid attack that manifests itself by the delithiation of the surface layer of the particles and the concomitant formation of LiOH and Li2 CO3 at the surface. This aging process occurred during the first few minutes, then it is saturated, and the thickness of the surface layer at saturation is 10nm. After aging, an initial discharge capacity of 139mAh/g was delivered at 1C-rate in the cut-off voltage of 3.0–4.3V. About 95% of its initial capacity was retained after 30 cycles.