Roy is an alchemist and a pretty good one at that. Alchemy basically means that he can turn one thing into something else as long as the amount of matter remains the same. This can go from turning a spoon into a fork to rebuilding a building that got destroyed. As long as he can determine the make up of an item, he can transmute it. Well that and he needs to draw a transmutation circle to guide the process (he usually has one already drawn on his gloves).

He rarely uses this type of alchemy in combat however, preferring his own particular brand of alchemy that earned him the title of "Flame alchemist". He wears a pair of spark cloth gloves that allow him to create a flame just by snapping his fingers. After that, he transmutes the density of the air around him to guide the flames. Using this technique he can set things on fire and create large explosions.