[en] Highlights: • A simple, cheap and environmental friendly method has been used to prepare Co-Fe-Al nanoparticles. • Small Co-Fe-Al particles with high saturation magnetization and low coercivity have been got. • The influence of pH value and atomic composition will shed light on the application of the method. Co-Fe-Al nanoparticles were synthesized by using a simple solution reduction method. The effects of pH value and atomic composition on the morphology, microstructure and magnetic properties of the prepared Co-Fe-Al nanoparticles were investigated. It was found that pure Co-Fe-Al phase with small particle size can be obtained at pH = 7.0 which have high saturation magnetization and low coercivity. Furthermore, the defects will increase with the increasing of Co composition in Co-Fe-Al nanoparticles which induce the deterioration of the B2 ordering, the abrupt decrease of magnetic moment and the abrupt increase of coercivity.