AbstractHere, we report the structure evolution, magnetic and ferroelectric properties in Co-doped 4- and 3-layered intergrowth Aurivillius compounds Bi₄NdTi₃Fe_1-xCo_xO₁₅-Bi₃NdTi₂Fe_1-xCo_xO_12-δ. The compounds suffer a structure evolution from the parent 4-layered phase (Bi₄NdTi₃FeO₁₅) to 3-layered phase (Bi₃NdTi₂CoO_12-δ) with increasing cobalt doping level from 0 to 1. Meanwhile the remanent magnetization and polarization show opposite variation tendencies against the doping level, and the sample with x = 0.3 has the largest remanent magnetization and the smallest polarization. It is believed that the Co concentration dependent magnetic properties are related to the population of the Fe³⁺ -O-Co³⁺ bonds, while the suppressed ferroelectric polarization is due to the enhanced leakage current caused by the increasing Co concentration. Furthermore, the samples (x = 0.1–0.7) with ferromagnetism show magnetoelectric coupling effects at room temperature. The results indicate that it is an effective method to create new multiferroic materials through modifying natural superlattices.