The effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the phase stability and evolution of morphology of La-doped Ni0.5Co0.5Fe2O4 nanopowders prepared via sol-gel auto-combustion method has been investigated. XRD analysis indicates the formation of single cubic spinel phases, while the crystallite size is found smaller when using cobalt acetate precursor. The Williamson-Hall plot has been used for estimating the crystallite size and lattice strain. SEM observations reveal homogenous and slightly agglomerated particles. EDS analysis confirms that the chemical composition was close to the nominal stoichiometry. The interionic distances cation-cation, cation-anion and bond angles have been calculated. FTIR spectra contain two absorption bands in the range from 400 to 600 cm(-1) which confirm the formation of the spinel structure.