Coffee grounds are a vegetable biomass that can be efficiently burned. The carbon dioxide generated by burning coffee grounds is affecting global warming. On the other hand, ammonia generated in the places such as toilets or farms produces a bad smell. In the present study, we have analyzed the possibility of ammonia elimination using the carbonaceous materials produced from coffee grounds. Carbonaceous materials were prepared by the microwave treatment of coffee grounds. We observed that the saturated amounts of ammonia adsorbed by some of the carbonaceous materials produced from coffee grounds were greater than that adsorbed by activated carbon. In contrast, the activated carbon adsorption rate for ammonia was higher than those of the carbonaceous materials. Therefore, carbonaceous materials produced from coffee grounds could be utilized for the removal of ammonia in the gaseous phase.