Abstract: In the Loess Plateau of China, the interface between the Loess and Hipparion Red Clay is widely distributed. The initial adhesion between this interfaces plays an important role in its shear strength. To investigate the effect of initial adhesion on shear strength and deformation characteristics of the interfaces, we firstly performed a series of direct shear experiments. Then, we discussed the effects of initial adhesion on failure mode, shear deformation and shear strength of interfaces. The results indicate that the failure modes of interfaces with initial adhesion and interfaces without initial adhesion are different. The initial adhesion improves the sliding resistance of specimen along the interface during shearing, and the failure mode of specimen tends to shear-off with higher damage. The shear stress- displacement curves of interfaces show strain softening shape, indicating the brittle failure of specimens. For interface specimens with initial adhesion, the displacement corresponding to peak strength and the dropping of shear stress after peak strength are greater than that of specimen without initial adhesion. The vertical dilatancy behavior of interfaces during shearing is obvious, however, the initial adhesion reduces the vertical dilatancy displacement of specimens. The variation range of dilatancy displacement of interface with initial adhesion is less than that of specimens without initial adhesion. The initial adhesion significantly improves the shear strength of interfaces. When the interface roughness is lower, the initial adhesion improve the shear strength of interfaces greatly. When the interface roughness is higher, the increment of shear strength of interfaces induced by initial adhesion decreases. This is because the shear strength of interfaces is mainly dominated by the shear strength of heterogeneous soils on both sides of interfaces.