The compounds Bi5FeTi3O15 (BFTO) and Bi5Fe0.5Co0.5Ti3O15 (BFCT) were prepared by incorporating BiFeO3 (BFO) and BiFe0.5Co0.5O3 (BFCO) into the host Bi4Ti3O12 (abbreviated as BFTO-1 and BFCT-1) and by the conventional solid-state reaction method (abbreviated as BFTO-2 and BFCT-2). X-ray analysis indicates a four-layer Aurivillius phases with an orthorhombic symmetry. At room temperature, the remnant polarization (2P (r)) of BFTO-1, BFTO-2, BFCT-1, and BFCT-2 samples are measured to be 11.0, 3.5, 13, and 6.3 mu C/cm(2), respectively, and the corresponding remnant magnetization (2M (r)) are about 2.72 x 10(-3) memu/g, 1.51 x 10(-3) memu/g, 7.6 and 2.1 memu/g, respectively. Both BFTO-1 and BFCT-1 samples exhibit the dielectric peaks at around 755 and 772 A degrees C in their epsilon-T curves, respectively.