Monodispersed Fe 3 O 4 nanoplates between two carbon films were synthesized by pyrolyzing ferrocene and sodium oxalate in a stainless steel autoclave of 64mL capacity at 600°C. The Fe 3 O 4 nanoplates are triangular single crystals, sometimes truncated, with edge lengths ranging from 50 to 100nm. In an experiment where the pressure of the reaction system was increased, carbon-encapsulated Fe 3 O 4 nanorods were obtained. The inner Fe 3 O 4 nanorods are also single crystal with a diameter ca. 100nm and lengths up to 1μm. A possible formation mechanism for the layered structure is proposed based on the experimental results. Magnetic property measurements show that the layered nanoplates display ferromagnetic properties at room temperature.