Nano-oxide　powders　of　LaCoO3　and　La0.5Nd0.5CoO3　were　synthesized　by　citrate　sol-gel　method.　Their　phase　constitutes　and　crystal　structures　were　characterized　by　IR-spectrum　and　powder　X-ray　diffraction,　and　the　phase-transition　due　to　Nd-doped　was　investigated.　XRD　analysis　indicates　that　single　perovskite　structure　is　created　when　the　precursors　are　calcined　over　600C,　and　that　the　increasing　calcined　temperature　does　not　change　phase　lattice　structures.　The　particle　sizes　of　the　complex　oxides　calcined　at　the　temperature　between　600C　and　900C　are　within　31-59　nm　calculated　by　Scherrer　formula.　These　cobaltate　series　oxides　are　found　to　undergo　a　phase　transition　from　rhombohedral　in　LaCoO3　to　cubic　symmetry　in　La0.5Nd0.5CoO3.　The　experimental　IR　spectra　at　428　cm-1　for　LaCoO3　and　450　cm-1　for　La0.5Nd0.5CoO3　show　the　difference　of　in-plane　vibration　of　Co-O　between　the　two　complex　oxides.　It　can　come　to　a　conclusion　that　phase　transition　is　mainly　due　to　the　change　of　octahedral　coordination　surrounding　of　Co　ion,　which　are　caused　by　the　lanthanum　contract　and　Nd　(III)　more　intensive　polarization.