An investigation was conducted into the correlation of microstructure and the cracking phenomenon that often occurred in hot-rolled lightweight steel plates. Two kinds of steels were fabricated with varying Mn and Al contents, and their microstructures, tensile properties, and high-temperature transformation behavior were investigated. In the two steels, banded structures containing ferrite grains and j-carbides were well developed along the rolling direction. Detailed microstructural analyses showed that cracks initiated at film-type j-carbides continuously formed interfaces between bands, while the band populated with j-carbides did not play an important role in initiating cracks. Thus, the formation of band structures and film-type interfacial j-carbides must be minimized to prevent the cracking. The decreased content of hardenability elements, including aluminum, higher finish-rolling temperature, reduced central segregation during the slabmaking process, and decreased material variation during hot rolling, were suggested as practical methods for preventing the cracking.