A catalyst for use in vapor phase oxidation of naphthalene into 1,4-naphthoquinone is dislosed. The catalyst which is supported on an inert carrier material is represented by the formula:(V)a(K)b(S)c(Fe)d(Sn)e(X)f(O)gwhere V, K, S, Fe, Sn and O stand for vanadium, potassium, sulfur, iron, tin and oxygen, respectively; X stands for at least one element such as silicon, titanium or aluminum which serves as a carrier in the form of oxide; and a, b, c, d, e, f and g are the atomic fractions of the respective elements wherein the ratio of a:b:c:d:e:f=10:10-100:5-100:0.1-10:0.05-10:10-300. Using the above catalyst the vapor phase oxidation can be effected at a relatively low temperature of not higher than 500.degree. C., usually not higher than 420.degree. C., resulting in the formation of 1,4-naphthoquinone in a high yield and with a high selectivity.