The synthesis of magnetic nano-sized spinel ferrites has become an important area of research, due to their several potential applications. In this work, CoFe2O4 nanoparticles were synthesized by the co-precipitation method. Structural, magnetic, and photocatalytic properties of cobalt ferrites were analyzed based on their chemical composition considering their biological properties. Structural and morphological properties were investigated by X-ray diffraction analysis (XRD) and scanning electron microscope (SEM), respectively. Lattice parameters and cell volumes were calculated from XRD data. SEM images revealed uniform surface morphology and spherical shape of nanoparticles. Magnetization measurements were measured by using Lake Shore 7304 model Vibrating Sample Magnetometer (VSM). In hemolytic activity tests, formation of a precipitate with a characteristic black color provided an explicit evidence to the formation of heme-iron complexes. Undesirable hemolytic effect of CoFe2O4 nanoparticles on human erythrocytes at both concentrations was attributed to the comparatively high amount of reactive oxygen species formed by CoFe2O4 nanoparticles. The theoretical concentration C-o (theory) obtained by second-order model (0.82 mg/L) fit with the experimental value of C-o (experimental) (0.95 mg/L) well in photocatalytic activity tests.