PURPOSE: To obtain anthraquinone useful as an intermediate for dyes or an additive for preparing paper or pulp, by reacting inexpensive toluene as a starting material with a gas containing oxygen in the vapor phase in the presence of a catalyst containing vanadium directly in one stage.

CONSTITUTION: Toluene (or a mixture containing slight amounts of benzene and xylene may be usable) is reacted with a gas containing oxygen in the vapor phase in the presence of a catalyst containing vanadium, preferably tetra- or penta-valent oxide of vanadium or a mixture of the tetra- with the penta-valent vanadium oxides) to give anthraquinone. The mixing ratio between the toluene and the air is preferably 1.2vol% or less or 7vol% or more in vol% of toluene vapor in the air, and the reaction is carried out at a temperature in the range of 300W400°C. The unreacted toluene after the reaction is recycled through the reaction system for reuse.