Abstract: Steel bars-glass fiber-reinforced polymer (GFRP) bars reinforced concrete (RC) beams combined the advantages of steel bars and GFRP bars. Flexural capacity was increased compared with RC beams and serviceability performance was improved compared with the pure fiber-reinforced polymer (FRP) reinforced concrete beams, however, the investigation of fatigue behaviors was limited. In this study, seven beams were fabricated for fatigue tests, and the test parameters were load amplitude, effective reinforcement ratio and area ratio of FRP to steel bars (A_f/A_s). The test results show that fatigue failure of the steel bars-GFRP bars RC beams start with fatigue fracture of steel bars and the fracture surface is significantly different from that of static tensile failure modes. Plane section assumption is verified under fatigue. The fatigue load amplitude has significant effects on the fatigue life. With the increase of fatigue load amplitude, strains in steel bars, GFRP bars and concrete increases, and the fatigue life decrease. The increase of effective reinforcement ratio contribute to decreasing mid-span deflection and crack width, and improve the serviceability. The increase of area ratio of FRP to steel bars (A_f/A_s) has negative effects on the fatigue behaviors of steel bars-GFRP bars RC beams. The fatigue life decrease from 366 thousand cycles to 83 thousand cycles with A_f/A_s increasing from 0.25 to 2.0. Different theoretical models for the mid-span deflection of beams under fatigue load are compared and the CEB-FIP 2010 presented satisfactory prediction, and thus is recommended.