Abstract. Sol-gel yttrium iron garnet films were prepared at different solution aging time and annealing temperature. Microstructure analysis using an X-ray diffractometer showed that aging time reduced the annealing temperature to crystallize the YIG thin films. The crystallite size increased with the aging and annealing time. The average particle size measured using a field emission scanning microscope is in the range of 19.62 to 49.12 nm. The thickness of the films were between 49.13 to 72.63 nm. The results from a vibrating sample magnetometer used to measure the magnetic properties showed that the magnetization saturation of the films increased with the increment of solution aging time.Keywords: Thin film, Yttrium Iron Garnet (YIG), sol-gel, aging. IntroductionYttrium Iron Garnet (YIG) is a well-known ferrite material that is widely used for microwave devices, magneto-optical devices and optical communication [3] have reported on the influence of pH value on the structure and magnetic properties of YIG thin films. They found that higher pH value produces film with bigger particle size and higher saturation magnetization. N.B Ibrahim et al. [8] have reported that the longest aging solution produces Zinc Oxide (ZnO) film with the best crystalline and optical properties. The film is also thick and has larger particle size. Ebru [9] has also reported that the aging solution of lead zirconate titanate, Pb(Zr x Ti 1-x )O 3 (PZT) can change the preferred orientation and decrease the electrical properties of the films. S.M Rozati [10] reported the aged solution affects the structure, morphology and optical properties of fluorine-doped ZnO film. The intensity of crystallinity peak and optical transmittance increases with the increasing aging time. For the particle size, it decreases with the increasing aging day solution. However, there is no report so far about the effect of solution aging on YIG thin film prepared by a sol-gel method. In this study, the effect of annealing temperature and aging time on the structural and magnetic properties of YIG thin films by a sol-gel method is reported. The YIG solution was aged for 0 (fresh), 2, 7 and 11 days with different annealing temperature, 700℃, 800℃ and 900℃. Experimental MethodYttrium Iron Garnet (YIG) thin films on quartz substrate were prepared using a sol-gel method followed by a spin coating technique. The compounds of yttrium nitrate hexahydrate, and iron nitrate