PURPOSE: To obtain 1,4-naphthoquinone economically, by gradually raising a heating rate or increasing O2 content in an O2-containing gas to cautiously regenerate a catalyst having lowered activity and catalytically oxidizing naphthalene with the O2-containing gas by the use of the regenerated catalyst.

CONSTITUTION: In obtaining 1,4-naphthoquinone by catalytically oxidizing naphthoquinone with O2-containing gas in vapor phase by the use of a derivative of vanadium pentoxide-potassium sulfate-potassium pyrosulfate system shown by the formula (X is Si, Ti, Al, etc.; aWg are atomic ratio of each element; a:b:c:d:e:f is 10:10W100:5W100:0.1W10:0.05W10:10W300; g is number determined by values of aWf), feed of a raw material to a catalyst having lowered activity is stopped and temperature of the catalytic layer is lowered to ≤300°C. Then the rate of heating of the catalytic layer is made ≤50°C/hr, the catalyst is more preferably heat-treated at 350W480°C, especially ≤380°C by gradually increasing O2 concentration of the gas to be sent to the layer and the reaction is restarted.