Co-Ti ferrite (Co(1+x)Ti(x)Fe(2-2x)O(4), 0.2 <= x <= 0.5) nanoparticles with average diameters ranging from 6 to 12 nm were produced by using our novel wet chemical method. The crystal structures and magnetic properties of the obtained samples were investigated by X-ray diffraction and superconducting quantum interference device (SQUID) magnetometer measurements. DC magnetization measurements showed that the coercive force H(c) and saturation magnetization M(s) decreased as the composite parameter x increased. This phenomenon suggests that Ti(4+) ions located on B-sites weaken the superexchange interaction between A and B sites. For x = 0.3, the value of H(c) decreased drastically. The AC magnetic susceptibility of these samples was also investigated, and it was concluded that the sample with a diameter of 12 nm and composition given by x = 0.3 is the most appropriate sample for use as an agent in hyperthermia treatment.