PURPOSE: To obtain naphthoquinone useful as a raw material for the synthesis of dyes and pharmaceuticals, etc., using a fluidized bed, in high efficiency and yield, by carrying out gaseous phase oxidization of naphthalene using a specific highly active catalyst for fluidized bed.

CONSTITUTION: The objective compound can be produced by the gaseous phase oxidization of naphthalene in the presence of a fluidizing catalyst having an average particle diameter of 30W100μ, containing particles of ≤120μ in diameter accounting for ≥80% of the whole catalyst and produced by supporting a catalyst component of formula I [aWf are atomic ratios of respective elements' a:b:c:d:e=10:(10W100):(5W100):(0.05W10):(10W500); f is a value dependent to the values aWe and the form of the oxide, etc.], e.g. the compounds of formula II, formula III, formula IV, etc., on a silica-containing carrier and calcining the supported catalyst component. The above catalyst can be prepared e.g. by mixing calcined ammonium metavanadate with K2SO4, adding water to the mixture to adjust its pH, mixing with a carrier such as finely pulverized silica, subjecting to heating, evaporation to dryness and calcination at 450°C for ≥5hr and controlling of the grain size without molding the catalyst.