One-dimensional magnetite particles were prepared by a seed-mediated growth method under magnetic field. The amount of seed, seed size, PolyvinylPyrrolidone concentration (PVP) and reaction time have a significant effect on the morphology of the samples. The addition of a small amount of 100nm seeds leads to obtain rod-like particles, while chain-like particles are formed when the seed size is increased to 700 nm. The aspect ratio of the rod is controlled by varying the volume ratio of seed to iron salt. Increasing the reaction time is favorable to the formation of chain-like particles.