The magnetic, dielectric, and magnetodielectric properties of bi-layered perovskite Bi4.25Gd0.75Fe0.5Co0.5Ti3O15 (BGFCT) ceramics were investigated. Weak ferromagnetism at room temperature with a remnant magnetization M (r) of 0.26 emu/g was found in the BGFCT specimens, and the ferromagnetic transition was determined at similar to 383 K. The change in valence state for magnetic ions has been confirmed by the XPS measurement, which would introduce ferromagnetism via double-exchange interaction. The Dzyaloshinsky-Moriya interaction was also proposed to explain weak ferromagnetism. The ferroelectric phase transition around 1072 K has been verified by the temperature-dependent dielectric measurement and differential scanning calorimetry. The standard positive-up-negative-down tests indicated the intrinsic ferroelectricity of BGFCT, and an obvious MD effect was observed in the temperature range from 190 to 280 K. The dielectric loss of the BGFCT exhibits one dielectric relaxation with activation energy E (a) similar to 0.49 eV, which is related to the hooping of oxygen vacancies.