The nanosize magnetic particles were synthesized by thermal decomposition method with size distribution in the range of 10 ~ 30 nm. Different category and quantity of surfactants were used modifying the surface of the synthesized nanoparticles to control the particles’ shape and size. Multi-shapes, such as uniformity cubic, mixture of spherical and cubic, and the similar chick footmarks, were acquired in our experiment by different surfactants. It indicates the surfactant is a key factor for the size and shape of particles. The surfactants of PVP and oleylamine made the particle shape be uniformity cubic; However, the particle partly behaved as spherical shape in the case of using PVP and oleic acid as surfactants.