Effective diffusivity for CO–CO2 gas mixture in Hot Briquetting Carbon Composite Iron Ore (CCB) at a temperature range of room temperature to 673 K was measured by Wicke–Kallenbach Method. The results obtained are summarized as follows;(1) Effective diffusivity of CO–CO2 gas mixture through CCB increased with increasing temperature and fractional reaction of CCB. The effective diffusivity for CO–CO2 system in CCB was proportional to the 1.50 power of temperature.(2) Kundsen diffusion and surface diffusion are negligible in regard to diffusions of CO and CO2 in CO–CO2 gas mixture in CCB. Therefore, diffusions of CO and CO2 in CO–CO2 gas mixture in CCB are described by molecular diffusion.