Electroreduction of - N = N - and - NO2 groups of azodyes, 1-(4-nitro phenyl) -azo-2-naphthol (A), 1-(3-nitrophenyl)azo-2-naphthol (B), 1-(2-nitrophenyl)-azo 2-naphthol (C) has been studied. The azo compound not containing - NO2 group taken for the study was 1-(2-hydroxyphenyl)-azo-2-naphthol (D). The studies were carried out in partial aqueous media containing organic co-solvents such as acetonitrile, DMF and methanol. The substituent effect on cathodic reduction potentials E-pc in case of dyes A, B, C were studied and it was found to be in increasing order i.e. E-pc(A) < E-pc(B) < E-pc(C). During electroreduction of dyes A, B, and C. two separate quasireversible peaks, one for reductive cleavage of - N = N - groups, the other one due to reduction of - NO2 group into - NH2 groups were observed. The redox process has been compared with the cyclic voltammetry of the trial compounds, 2-nitroaniline and 4-amino-3-hydroxy naphthalene-1-sulphonic acid. The other data such as effect of pH, concentration of active species, supporting electrolyte, scan rate on cathodic reduction peak potential and cathodic peak,current has been determined. The process is found to be diffusion controlled.