Perovskite-type oxide nanocrystalline LaCoO3-λ was prepared using the citrate method.The structure and morphology of the sam-pies were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM).The intermediate products were analyzed by thermal gravimetric and differential thermal analysis (TG-DTA) technology.The results showed that nanocrystaUine LaCoO3-λwith a granula of 30-50 nm had a cubic perovskite structure.The reaction mechanism of low temperature preparation was suggested as fol-lows:the metal complex was first formed by the combination of metal ion and citric acid;and then it decomposed into an aconitie acid com-plex, followed by an oxycarbonate,and finally a perovskite-type oxide.