To obtain an azo compound by a process advantageous from the operational and economical points of view by dispersing solid particles of a phenolic compound in water in the presence of a surfactant and subjecting the phenolic compound to a coupling reaction.

(A) A phenolic compound exhibiting solid particle form is made to react with (B) diazonium salt of an aromatic aniline compound in the presence of (C) a surfactant in water to obtain (D) the objective azo compound. Preferably, the component A is a phenolic compound of formula I (R1 is H, a 1-12C alkyl, a 5-6C cycloalkyl, phenyl, etc.; R2 is H, a halogen, OH or a 1-4C alkoxy; R3 is a halogen, a 1-12C alkyl, a 5-6C cycloalkyl, a 1-4C alkoxy, phenyl, etc.), the component B is an aromatic aniline compound of formula II (R4 is H, a halogen, a 1-12C alkyl, carboxy, etc.) and the component D is an azo compound of formula III.