Abstract: Stainless steel samples were made by Powder injection Molding (PIM) process with -400 mesh powder in order to investigate the sintering mechanism in this system and develop the PIM of stainless steels. The process included mixing, injection molding, debinding and sintering. Neck growth model was used to analyze the sintering mechanism. The results show that lattice (volume) diffusion is the main mechanism in the sintering process, the products with higher density (>95%) and properties are obtained. At lower temperatures, grain boundary diffusion may play a role in the sintering densification.