An azo compound which in the free acid form is represented by the following formula: ##STR1## where R.sub.1 stands for methyl, ethyl, R.sub.2 stands for hydrogen, methyl, methoxy or ethoxy, R.sub.3 stands for hydrogen or methyl, and K stands for ##STR2## wherein the benzene nucleus A may be further substituted by methyl, amino, acetylamino or methoxy or: ##STR3## wherein these naphthalene neuclei may be further substituted by hydroxy, amino or acetylamino, also a process for preparing the azo compound and a dyeing method using said azo compound.