Polycrystalline Co-ferrite was produced by modified citrate gel method. Samples were afterward heat treated at different temperatures upto 1300°C. The XRD pattern shows that all samples exhibit a single phase spinel structure and improvement and sharpness in intensity of peaks with increasing annealing temperature. Measurement of hysteresis loops demonstrate that after the heat treatment a saturation magnetization of 60- 84 emu/g is obtained. Measurements of the longitudinal magnetostriction gave values between 20 ppm and 130 ppm. Magnetostriction increases gradually with increase in annealing temperature and becomes highest when the saturation magnetization values are larger.