Hybrid films composed of poly(luminol) and nanometer-sized clusters of polyoxometalate, SiMo 12O 40 4− and PMo 12O 40 3− have been prepared in acidic aqueous solutions. These films are stable and electrochemically active, and produced on glassy carbon, platinum, gold and transparent semiconductor tin oxide electrodes. The electrochemical quartz crystal microbalance and cyclic voltammetry were used to study in situ growth of the hybrid poly(luminol)/SiMo 12O 40 4− and poly(luminol)/PMo 12O 40 3−. Both the poly(luminol)/SiMo 12O 40 4− and poly(luminol)/PMo 12O 40 3− hybrid films showed four redox couples and the electrochemical properties were compared to SiMo 12O 40 4− and PMo 12O 40 3−. When transferred to various acidity aqueous solutions, the four redox couples and the formal potentials of two hybride film were observed to be pH-dependent. The electrocatalytic reduction of ClO 3 −, BrO 3 −, IO 3 −, S 2O 8 2− and NO 2 − by a poly(luminol)/PMo 12O 40 3− hybrid film in an acidic aqueous solution showed an electrocatalytic reduction activity of IO 3 − > BrO 3 − and ClO 3 −. The electrocatalytic oxidation of dopamine and epinephrine by a poly(luminol)/PMo 12O 40 3− hybrid film was also investigated.