Abstract: The soil is easy to peel off when the external-soil spray seeding (ESSS) technology is used to restore the high and steep bare rock slope. The application of microbial mineralization technology to form microbial mortar on bare rock surface has the potential to improve the adhesion and stability of sprayed soil substrate and rock surface. The interfacial shear tests on the limestone cemented by microbial mortar are carried out to investigate the change of shear strength and cementation mechanism of the interface between microbial mortar and rock. The results show that the cohesion and friction angle of the microbial mortar-rock interface can reach 45.6 kPa and 26.40˚, respectively. The microbial cementation has few effects on the friction angle of the interface. When the calcium carbonate content is higher than 2.5%, the microbial mortar has better water stability. There are abundant pore in the microbial mortar overlying the rock surface. The shear failure of interface is mainly caused by the peeling of the contact surface between the sand particles and the calcium carbonate crystals, and the internal fracture of the calcium carbonate crystal aggregate. The research results can provide reference for the application of microbial geotechnical technology in the ecological protection of rock slopes.