The Fischer-Tropsch synthesis is a catalytic conversion of syngas into hydrocarbon mixtures. A solvothermal method was used to prepare Iron-cobalt-cerium nanocatalyst for conversion of syngas into light olefins. Duration of aging time in preparing method is a key factor affecting in a chemical process. The results showed that the optimal aging time and operating temperature in order to increase light olefin selectivity is at 11 h and 330 A degrees C. The effects of experimental variables including aging time (5, 8 and 11 h) and operating temperature (270-380 A degrees C) were investigated. The nanocatalysts were characterized by temperature programed-reduction (TPR), X-ray diffraction (XRD), energy dispersive X-ray, Fourier infrared spectroscopy, and vibrating sample magnetometer. TPR profiles of the nanocatalysts synthesized at different time of aging indicated that aging time shifted the sample's reducibility via affecting its particle size. Average crystalline size determined from XRD patterns ranged over 4.5-6.6 nm. It is found that particle size increases with increasing aging time. The results show that time of aging has effect on magnetic properties of nanocatalysts changing from soft ferromagnetic to a hard ferromagnetic one as aging time increases. In addition, the sample aged for 5h exhibits a maximum saturation magnetization of 7.768 emu/g, the maximum coercivity value of 1744.46 Oe is obtained for the sample aged for 8 h.