In this work firstly carbon quantum dots were prepared by using turmeric as a green starting materials. Hydrothermal method was used as an effective method for preparation of product with preferential growth. Finally, CoFe2O4 and magnetic cobalt ferrite–carbon nanocomposite were synthesized. To the best of our knowledge, this is the first work that carbon quantum dots were prepared form biocompatible and cost effective turmeric precursor. The effects of time and temperature on the morphology and particle size were investigated. Nanostructures were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, ultra violet–visible absorption and photo-luminescence spectroscopy. The prepared product show suitable photo-luminescence under ultraviolet irradiation. Vibrating sample magnetometer shows ferromagnetic property of the both CoFe2O4 and cobalt ferrite–carbon nanocomposite. Photocatalyst property of the magnetic nanocomposite was investigated by degradation of three azo dyes (acid black 24, acid brown 14 and acid red 1) under ultra violet irradiation. The results confirm that green synthesized nanocomposites show applicable photoluminescence and photocatalyst properties.