Coke produced with 7.5 wt % charcoal addition and its base blend coke were subjected to gasification and annealing simulating the conditions within an iron-making blast furnace (BF). The changes in the pore structure of cokes during gasification and annealing were studied using image analysis to understand the effect of charcoal addition on pore structure development and degradation mechanism of coke under blast furnace operating conditions. The addition of charcoal had no significant effect on the coke pore structure during blast furnace annealing; the similar behaviors between cokes were mainly attributed to the carbon-mineral reactions that took place equivalently in both cokes. However, gasification in blast furnace caused a greater change in bio-coke pore structure, and this extra change in pore structure during gasification associated with charcoal addition was due to the preferential consumption of charcoal particles by the Boudouard reaction. Coke degradation under the BF conditions is directly related to the change in its pore structure and microstrength. Coke microstrength was not significantly impacted by charcoal addition; the greater degradation of bio-coke during BF gasification was due to the extra change in its pore structure.