An aroma diffuser includes a housing, a burner, a thermal conducting device and a hollow annular fragrance capsule. The burner and the thermal conducting device are combined in the housing. The thermal radiation of the thermal conducting device can be continuously and effectively transmitted to the donut-shaped fragrance capsule and the fragrance substance to quickly produce a stable aroma. The fragrance capsule is provided with a breathable film that prevents the fragrance substance from flowing to the outside of the fragrance capsule to contaminate the burner or the surroundings. The breathable film is formed of a fixing film and a microporous film. The fixing film combined with the microporous film is not deformed or ugly when heated, and the aroma can be diffused outward from the breathable film. The fragrance substance can be quickly replaced with another fragrance capsule after use.
