<p>In this study, the microbial-induced calcium carbonate precipitation (MICP) technology was used to grout and reduce the permeability of the fissures in limestone and granite. The effectiveness of the MICP under different conditions in permeability reduction in different lithologies were comprehensively investigated through lab tests. Three influential factors of interests include the grouting flow rate, the concentration of the cementing solution, and the concentration of the bacterial solution (OD₆₀₀). The indications of the effectiveness of the permeability reduction investigated in this study include the amount of CaCO₃ generated, the area proportion of the generated CaCO₃, and the thickness of the generated CaCO₃, the accumulation density in the fissures and the filling rate. It was found that the effect of lithology on the permeability reduction effectiveness is more significant under lower grouting flow rates, lower cementing solution concentrations, and higher bacterial solution concentrations. The better compatibility between the limestone fissures and the CaCO₃ particles leads to a faster CaCO₃ deposition rate compared with that in the granite, resulting in more CaCO3 accumulation, the permeability in limestone fractures is lower than that in granite fractures. And the lithology difference makes the planar and spatial accumulation forms of the generated CaCO₃ in the two fissures different, which is reflected in the proportion of the coverage area, the accumulation thickness and the accumulation density. In addition, a fitting and comparative analysis was carried out on the generated CaCO₃ in the fissures of limestone and granite, and it was found that the proportion of the CaCO₃ coverage area has a significant impact on the permeability reduction effect in the limestone fissures; while the mass of CaCO₃ has a significant impact on the permeability reduction effect in the granite fissures.</p>