Abstract: Based on the analysis of mechanical properties, chemical composition and metallographic examination, the causes of bending fracture of HRB400E hot-rolled ribbed steel bars were analyzed. The studies showed that the manganese content in chemical composition was relatively high. The presence of bainite and coarse grains in the structure was the main cause of bending fracture of the steel bars. The proper reduction of manganese content could effectively avoid the formation of bainite and coarse grains to guarantee the excellent mechanical properties of ribbed steel bars.