Abstract: The field pseudo-static tests on 4 full-scale reinforced concrete cast-in-situ bored piles with different reinforcement ratios are performed at a typical soft soil site of Tianjin. The seismic behavior indice, such as hysteretic behavior, energy dissipation, stiffness degradation, displacement ductility and bearing capacity of the test piles with different ratios of reinforcement under horizontal low cyclic loading, are studied. The results show that the equivalent viscous damping coefficients of four piles mainly appear between 0.10 to 0.23, and the displacement ductility coefficients of four piles are all above 4.5, indicating good energy dissipation and ductility. Increasing reinforcement ratio does not significantly improve the stiffness degradation process of the cast-in-situ bored piles and does not slow down the rate of stiffness degradation. Increasing the reinforcement ratio can effectively improve the plastic deformation capacity of the piles, and increase their ultimate displacement, and significantly increase the yield load and ultimate load of a single pile. Both the energy dissipation capacity and the displacement ductility of the piles increase firstly and then decrease with the increase of the reinforcement ratio, and based on the seismic performance of cast-in-situ piles, the recommended value of the optimal reinforcement ratio of cast-in-situ bored piles is 0.63%.