In this study, Al 2 O 3 /Nb ceramic matrix nanocomposite was synthesized by mechanical alloying, through mechanochemical reaction between Nb 2 O 5 and Al. Structural and phase evolution during mechanical alloying was studied by employing X-ray diffraction (XRD) and differential thermal analysis (DTA) techniques. It was found that the reaction between Al and Nb 2 O 5 takes place in an explosive mode after 170min of milling time. The milled powder had a microstructure consisting of nanocrystalline Al 2 O 3 base adjacent to Nb particles with a nanoscale grain size. At longer milling times, the intensity of Al 2 O 3 and Nb peaks decreased and became considerably broader due to the decreasing in crystallite size. After 15h of milling time, crystallite sizes of Nb and Al 2 O 3 were about 8 and 10nm, respectively. From DTA results, it was revealed that milling for 2h decreases the temperature of reaction between Nb 2 O 5 and Al from 910°C to 492°C.