Samples of Ni-doped CoFe₂O₄ nanoparticles (NPs) was synthesized by a sol-gel route to discuss doping effect on the photocatalytic performance. The spinel crystal structure of prepared samples was confirmed by XRD and also the crystalline size was calculated. XRD results show that the resulting nanoparticle crystal system is cubic with Fd-3m space group. Based on Rietveld's analysis, it is known that there is a decrease in the lattice parameters along with the addition of Nickel substitution content. FTIR results show absorption peaks in the octahedral and tetrahedral sites. In the image of the SEM results, it is known that agglomerates and irregularities occur in all samples. M-H curve indicates that saturation magnetization and the coercivity value tends to decrease when doping concentration of nickel was increased. In addition, the photocatalytic performance of cobalt ferrite-doped nickel stated that there was an increase in the degradation of methylene blue dye along with the increase in samples irradiation time. It is also seen that the photocatalyst performance increases with the addition of nickel.