This paper describes microstructure characteristics of MgAl2O4 thin films were deposited by sol-gel method with various annealing temperatures. Particular attention will be paid to the effects of an annealing treatment in air ambient on the physical properties. The annealed films were characterized using X-ray diffraction. The surface morphologies of annealed film were examined by scanning electron microscopy and atomic force microscopy. The dependence of the dielectric properties and microstructure characteristics on annealing temperature was also investigated.