The present invention is concerned with a novel azo compound represented by formula (1), (2) or (3), a water-soluble dye comprising this azo compound, and a polarizing film containing this azo compound. The obtained polarizing film has high hydrothermoresistance and a high polarization degree and is excellent in optical characteristics: ##STR1## wherein each of R.sub.1, R.sub.3 and R.sub.12 is independently a hydrogen atom, halogen atom, hydroxyl group, alkyl group having 1 or 2 carbon atoms, or alkoxy group having 1 or 2 carbon atoms; each of R.sub.2, R.sub.4, R.sub.8 and R.sub.9 is independently a hydrogen atom, hydroxyl group, alkyl group having 1 or 2 carbon atoms, alkoxy group having 1 or 2 carbon atoms, or acetylamino group; R.sub.5 is a hydroxyl group or amino group at the o-position or p-position to the azo group; each of R.sub.6 and R.sub.10 is a hydrogen atom, carboxyl group, or alkoxy group having 1 or 2 carbon atoms; each of R.sub.7 and R.sub.11 is a hydrogen atom, hydroxyl group, amino group, methylamino group, .beta.-hydroxyethylamino group, acetylamino group, or phenylamino or benzoylamino group in which the phenyl nucleus may be substituted by a nitro group, amino group, hydroxyl group, alkyl group having 1 or 2 carbon atoms, carboxyl group, sulfonic group or chlorine atom; p is 0 or 1; and q is 0, 1 or 2.