Coke strength is the most important characteristic for retaining permeability in the bed of a blast furnace. In the present study, coke was coated with phenolic resin in order to improve the coke strength, and a nanoindentation method was used to estimate the strength of the coated coke after reaction under CO2 atmosphere. The elastic modulus was measured for the microporous coke substrate,. The elastic modulus of coated coke before reaction was higher than that of uncoated coke. However, after reaction with CO2, the elastic modulus did not necessarily show an improvement in coke strength. The mechanism whereby the resin coating improved coke strength before and after the reaction was considered by a finite element analysis using a mesh superposition technique.