Abstract In this present work, spinel cobalt ferrite nanoparticles (CoFe2O4 NPs) and activated carbon-CoFe2O4 nanocomposites (AC-CoFeO4 NCs) were synthesized by simple co-precipitation method and used for photocatalytic dye degradation (PCD) of rhodamine-B (Rh-B) dye. The antimicrobial study of the as-synthesized CoFe2O4 NPs was also performed. The as-synthesized CoFe2O4 NPs and AC-CoFe2O4 NCs were analyzed by ultraviolet spectroscopy (UV), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) studies, scanning electron spectroscopy (FE-SEM) techniques. Powder XRD analysis showed that the as-synthesized CoFeO4 NPs and AC-CoFeO4 NCs had average particle size of 18 nm and 46 nm, respectively. The FE-SEM showed that the CoFe2O4 samples have sphere like morphology and were well decorated on activated carbon in order to provide high surface area. AC-CoFe2O4 NCs have effectively used for the PCD of Rh-B dye with high efficiency. Furthermore, spinel CoFe2O4 NPs acted as a more effective antimicrobial agent against Gram-negative and Gram-positive bacterial strains. Moreover, AC-CoFe2O4 NCs can be used as the precursor materials for supercapacitor, sensors etc.