$Y_{2.5}La_{0.5}Fe_5O_{12}$ is fabricated by a sol-gel method and the magnetic properties of single phase garnet are investigated by using X-ray diffraction, vibrating sample magnetometer, scanning electron microscopy and M$"{o}$ssbauer spectroscopy. The single phase powders garnet was fired at 100$0^{circ}C$ for 8 hours. The crystal structures of samples are cubic garnet. Mossbauer spectroscopy were measured from 13 K to 750 K. M$"{o}$ssbauer spectra show that the iron exist ferric trivalence in sample. The spin wave constants were determined $B_{3/2}=0.32{pm}0.05,; C_{5/2}=0.18{pm}0.05$ and Debye temperature were determined 382 K at 24(d) site and 246 K at 16(a)-site. The saturation magnetization $M_s$ of powder is 25 emu/g. 25 emu/g.