Nanocrystalline α-Al2O3 powders were synthesized by low temperature combustion technique using aluminum nitrate-urea reactive system. The relationship between the color of powders and the mass ratio of aluminum nitrate-to-urea was investigated. X-ray results showed presence of the well-crystallized α-Al2O3 after calcined at 1100oC for 2h with 2.5:1 mass ratio. The grain size of α-Al2O3 powders was calculated by Scherrer equation. TEM observation and Clouter N4 Plus measurement results showed that the particle size distributed from 20 nm to 70 nm.