Ultrafine Ni0.1Co0.9Fe2O4 nanocrystals were synthesized by the simple co-precipitation route, and well-accurately characterized by X-ray diffraction (XRD), FT-IR spectra, and high resolution transmission electron microscopy (HTEM) technique. XRD investigation proved the evolution of the single-phase cubic spinel structure for these nanocrystals. The fine crystallite size R average value was 36.265 nm. FT-IR absorption spectra displayed the essential absorption bands that were related to their principle sites and main bonds. All the deduced parameters were affected by the presence of the Ni2+, Co2+, and Fe3+ cations in these nanocrystals. HTEM images showed accumulations for the nanoparticles, where the average particle size value was 42.9 nm and was slightly higher than the crystallite size R. Evaluation of photocatalytic activity for Ni0.1Co0.9Fe2O4 Nano-ferrites was obtained through the degradation of Crystal Violet (CV) dye (1 × 10-5 M) in aqueous solution under visible light irradiation using 100 Watt Tungsten lamp fixed at ~ 10 cm distance. As a result, usage of these new ultrafine Ni0.1Co0.9Fe2O4 nanocrystals gives a new marvellous route for the advancement of cost-effective technologies for quite good waste water recycling models, for raising water quality and for the promotion of fruitful efforts in improving treatment systems.