The　NaInO2　nanoparticles　were　prepared　by　solid　state　reaction　using　Na2CO3　and　In2O3　as　raw　materials.　The　products　were　characterized　by　X-ray　diffraction(XRD),　scanning　electron　microscopy(SEM)　and　UV-Vis　diffuse　reflectance　spectroscopy(DRS).　The　influence　of　n(Na2CO3)/n(In2O3)　and　calcined　temperature　on　structure　and　morphology　of　products　were　studied.　The　photocatalytic　activity　was　evaluated　by　photocatalytic　degradation　of　formaldehyde.　The　results　show　that　the　pure　rhombohedral　phase　NaInO2　particles　were　obtained　at　the　conditions　of　750　°C　calcined　temperature.　The　optimal　ratio　n(Na2CO3)/n(In2O3)　was　2.Diameter　of　the　NaInO2　particles　was　33.6　nm.　The　degradation　rate　of　formaldehyde　over　the　NaInO2　particles　was　48%　after　6　h　under　visible　light　irradiation.