Cu(In,Al)Se-2 films have been fabricated by electrodeposition technique in chloride solutions with sodium dodecyl sulfate (SDS) additive. The effects of SDS additive on the reduction potentials of Cu2+, In3+, Al3+ and H2SeO3 were studied by cyclic voltammerty. The corresponding chemical reactions were defined according to the XRD analysis. SDS additive promotes the deposited potential of each element closing to each other for abetter co-elecorodeposition environment. Besides, the chemical mechanism of Cu(In,Al)Se-2 films were investigated by chronoamperometry. The nucleation mechanism of Cu(In,Al)Se-2 films change from instantaneous nucleation to progressive nucleation as SDS additive is added. Scanning electron microscopy and energy dispersive X-ray spectroscopy reveal the surface morphology and stoichiometry of Cu(In,Al)Se-2 films at various potentials from -0.5 V to -1.0 V. The excess indium content inhibits the aluminum's incorporation into Cu(In,Al)Se-2 films, and induces the surface morphology to change from round-like structure into cauliflower-like structure. Raman spectra shows the quality and composition phase of Cu(In,Al)Se-2 films at various potentials. The shift in the optical band gap evidences the incorporation of aluminum element into CuInSe2 structure to form Cu(In,Al)Se-2 film. The corresponding optical bandgap of Cu(In,Al)Se-2 film with the composition Al/(In+Al) = 0.219 is about 1.17 eV. (C) 2013 The Electrochemical Society. [DOI: 10.1149/2.029304jes] All rights reserved.