The effect of the micro-internal stress which is induced in the ferrite grain by plastic constraint, on fracture behavior was investigated. The specimen used has combined microstructure with matrix of ferrite encapsulated by second phase of martensite. The micro-internal stress in the ferrite grain was estimated using a simple mechanical model, and its effect on micro and macro fracture behaviors was discussed. The results obtained are summarized as follows; The micro-internal stress promotes the formation of cleavage cracks in the ferrite during deformation. Consequently, it was concluded that the internal stress is one of the significant factors which cause the fracture ductility to decrease.