A solid-state reaction process has been developed to synthesize perovskite-type LaCoO3 nanocrystals with grain diameters of 15-40 nm. In the first step of the preparation, similar to5 nm composite hydroxide nanoparticles are synthesized by the solid-state reaction of La(NO3)(3).nH(2)O and Co(NO3)(2).6H(2)O with KOH at ambient temperature. A perovskite-type rhombohedral LaCoO3 phase appears at 550degreesC, after the hydroxide has been calcined at various temperatures. The phase transformation process is complete at similar to800degreesC, yielding a single-phase binary oxide. The results indicate that the new process is convenient, inexpensive, and effective for obtaining LaCoO3 nanocrystals with high yield.