Large-scale, uniform, monodisperse LaCO3OH cherry-blossom-like nanogears and/or nanocubes have been synthesized under hydrothermal reaction conditions. Upon the addition of only 5 mol% Ca2+ ions into a La nitrate salts solution with pH 8.5, LaCO3OH crystals with novel cubic or nanogear structures are formed in the hexagonal phase. The hydrothermal reactions were carried out without the addition of a template or catalysts. Both 24 hour and 48 hour hydrothermal reactions yield 100% pure LaCO3OH with no irregular particles. We examined the photoluminescence properties of the as-synthesized powders of the pure LaCO3OH nanogears and found one broad emission band centered at 394 nm after excitation at lambda = 280 nm. The NO reduction activity was also examined over highly dispersed CaO-containing La2O3 obtained after calcination the LaCO3OH at 800(o)C for 2hours. The CaO-containing La2O3 catalysts showed good stability for NO reduction with CH4 in the presence of O-2 and H2O vapor.