The addition of phosphoric acid to W-Nb-O catalyst active for glycerol transformation to acrolein and to W-V-Nb-O catalyst active for direct transformation of glycerol to acrylic acid appreciably improved their catalytic performance. The phosphoric acid-added W-Nb-O catalyst gave acrolein yield of 81.8%, and the phosphoric acid-added W-V-Nb-O catalyst gave acrylic acid yield of 59.2% in the direct glycerol transformation. The improvement of the catalytic performance seems due to the increases of the acid amount and the Bronsted acidity.