<p>The durability of materials treated with the microbiologically induced calcium carbonate precipitation (MICP) technique has garnered increasing attention in the field of geotechnical engineering. A series of studies have been reported on the durability of biotreated soils, but relatively little attention has been focused on the durability of MICP-treated rock fractures, especially on the microscopic degradation characteristics. In this study, surface characterization, mass measurement, Brazilian splitting tests, and nitrogen adsorption tests were conducted on the specimens subjected to dry–wet cycles to investigate the multiscale degradation characteristics of sandstone with biotreated fractures. The surface of the specimen displayed loss of fines and dissolution of calcium carbonate with increasing number of dry–wet cycles, which resulted in decreasing mass, reducing tensile strength, and increasing specific surface area. The different trends in the variations of the surface fractal dimension and pore-structure fractal dimension indicate that the increase in micropores and complexity of pore structure are the main characteristics in the early stages of dry–wet cycling, followed by a significant increase in surface roughness. This study suggests the benefits of early repair for the sustainability of MICP-treated rock fractures in dry–wet cycle environments.</p>