Multiferroic ceramics of Bi5Fe1-xCo x Ti3O15(x=0.0—0.6) are synthesized by the conventional solid state reaction, and their microstructure,magnetic and ferroelectric properties are investigated. X-ray diffraction patterns show that a four-layer Aurivillius phase is formed in each sample with a suggested structural transformation at heavy doping of Co ions. The Raman results demonstrate that Co ions enter into the lattice,occupy the B-sites in the BFCT-x and have an effect on the order occupancy of cations at B sites. It is found that the Co ion modification induces remarkable ferromagnetism (FM) at room temperature with a greatest remanent magnetization (2M r) of 2.3 memu/g at x=0.5,which is three orders of magnitude larger than that of Bi5Ti3FeO15(BFTO). All samples with Co doping have ferroelectricity (EM). The remanent polarization (2P r) reaches a value of 11 μC/cm2 at x=0.1,which is about 38.2% higher than that of BFTO,and then decreases when 0.2≤x≤0.4 and increases again at x=0.5 and 0.6. Of all materials,the sample of x=0.5 is best in both good FE and FM.