Sr₂FeMo_1-xNb_xO₆ (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0) samples were prepared by a conventional ceramic method. The samples were sintered in 3 %H₂/N₂ gas at 1100°C for 6 hours. Analysis of the X-ray data shows that the samples are of single phase in double perovskite. The magnetization and the conductivity values are found to decrease with increasing x. Whereas, the Seebeck coefficient is found to increase with respect to x in all compounds.