The experiment was carried out for the purpose of studying the carburization of pure iron ingot and sintered iron powder by solid carbon in the atmosphere of $N_2$ gas. The velocity of carburization was estimated by the diffusion coefficient D calculated by carburization equation. The results obtained were as follows ; 1. The briqueted sample of iron fine powder which made by higher pressure, carburization depth and carbon concentration were increased as much, and pure iron shelved the maximum value. 2, The higher the carburization temperature, carburization depth and carbon concentration were increased, and the melting zone which had 3.0~3.3%C at the interface of carburization was formed at 130$0^{circ}C$. As the pure iron ingot was carburized, the diffusion coefficient D of carbon were 0.211$ imes$$10^{-6}$$ extrm{cm}^2$ㆍsec$^{-1}$ at 120$0^{circ}C$ and 0.391$ imes$$10^{-6}$$ extrm{cm}^2$ㆍsec$^{-1}$ at 130$0^{circ}C$, respectively. 4. As the sintered iron powder was carburized at the pressure of 4 ton/$ extrm{cm}^2$, the diffusion coefficient of carbon were 0.157$ imes$$10^{-6}$$ extrm{cm}^2$ㆍsec$^{-1}$ at 120$0^{circ}C$ and 0.103$ imes$$10^{-5}$$ extrm{cm}^2$ㆍsec$^{-1}$ at 130$0^{circ}C$, respectively.