Using a microscopic model and the replica method as well as the Green's function theory, we have investigated the relaxor and multiferroic behavior of CdCr 2 S 4. The magnetization, the remanent polarization P r and the real part of the dielectric function ′ are studied theoretically as a function of temperature, with and without a magnetic field, respectively. The magnetization and the polarization exist together below the magnetic phase transition temperature. P r decreases whereas ′ increases and the peak shifts to smaller temperature values with increasing magnetic field h. Moreover, the temperature and electric field E dependence of the magnetization M is also discussed. A kink is observed around the ferroelectric transition temperature. The kink is deeper for stronger electric fields and anharmonic spin-phonon interactions.