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 CO gas. The volocity of carburization was estimaed by the diffusion coefficient D calculated by carburization equation. The results obtained were as follow: 1. The higher the carburization temperature, carburization depth and carbon concentration were increased, and the melting zone which had 2.8∼3.4%C at the 3∼4㎜ from interface of carburization was formed at 1300℃. 2. The main caxburization mechanism of pure iron ingot and the sintered iron powder were proceeded by CO gas up to 1100℃, solid carbon over than 1300℃, respectively. 3. The main carburization mechanism of pure iron ingot at 1200℃ was proceeded by solid carbon, and sintered iron powder was proceeded bs CO gas, however, in case the reaction time, the carburization was proceeded by solid carbon over than 5hrs. 4. The diffusion coefficient D of carbon were 0.559×10＾(－6)㎠.sec＾(－1) at 1100℃, 0.237×10＾(－6)㎠.sec＾(－1) at 1200℃, 0.087×10＾(－6)㎠.sec＾(－1) at 1300℃, in case of pure iron ingot carburized. 5. The diffusion coefficient D of carbon were 0.124 ㎠.sec＾(－1) at 1100℃, 0.102 ㎠.sec＾(－1) at 1200℃, 0.480×10＾(－6)㎠.sec＾(－1) at 1300℃, in the case of sintered iron carburized at the pressuring 4ton/㎠.