PROBLEM TO BE SOLVED: To provide an improved catalyst for various chemical processes, containing a heteropoly acid carried on a polyoxomethalate salt. SOLUTION: This heteropoly acid/oplyoxomethalate catalyst comprises a catalyst composition containing a heteropoly acid carried on a polyoxomethalate carrier, wherein the carrier of the polyoxomethalate is subjected to heat treatment at 385-600 deg.C. The heteropoly acid has a structure represented by the formula I, H(e'-bz')Gb-(Xk'Mm'-x'M1x'M2n'Oy')-e' (wherein G is an element selected from group 1-16 elements, or its oxygen; X is an element selected from group 3-16 elements; M is molybdenum, tungsten, or their combination; M1 is vanadium; M2 is a transition metal different from M and M1; z' is a charge of G; (b) is an integer of 0-12; k' is an integer of 1-5; m' is an integer of 5-20; x' is an integer of 0-6; n' is an integer of 0-3; y' is an integer of 18-62; and e' is a charge of polyoxomethalate anino). The polyoxomethalate carrier has a structure represented by the formula II, CaH(e-az)(XkMm-xM1xM2nOy)-e (wherein C is a cation selected from potassium, rubidium, cesium, magnetisum, calcium, strontium, barium, transistion metal, an actinide metal, a lanthanide metal, a metal oxyion, ammonium, tetraalkylammonium, pyridinium, quinolinium, a protonated aromatic amine, and a protonated aliphatic amine or a mixture thereof; (x) is an element selected from group 3-16 elements; M is molybdenum, tungsten, or their combination; M1 is vanadium; M2 is a transition metal different from M and M1; (z) is a charge of C; (k) is an integer of 1-5; (m) is an integer of 5-20; (n) is an integer of 0-3; x is an integer of 0-6; (y) is an integer of 18-62; and (e) is a charge of a olyoxomethalate anion). The polyoxomethalate carrier is, for example, Cs3PMo12O40, and the heteropoly acid is, for example, H3PMo12O40.