Cytotoxicity test is a rapid and standardized in vitro method to determine the harmful effects of materials used for biomedical purposes, such as drug carriers, implants and their coatings, biosensors and surgical/medical devices. In the present study, sol-gel driven nickel ferrite (NiFe2O4) and cobalt ferrite (CoFe2O4) nanoparticles (10-25 nm) at different concentrations were incorporated into biodegradable polymer, poly(lactic-co-glycolic acid) (PLGA), using oil-in-oil emulsion/solvent evaporation technique, and then the cytotoxicity of magnetic nanocomposite spheres was characterized using raw cells. The test provides the toxicity of the products prior to their real applications, which may limit animal experimentation, remove potential toxic compounds and reduce the downstream costs. The cytotoxicity results showed that both magnetic nanocomposite spheres were toxic at some degree to the raw cells; however, the cobalt ferrite nanoparticles in nanocomposite spheres are more toxic than the nickel ferrite nanoparticles.