Abstract: Long-term seasonal freeze-thaw weathering along the sandstone-mudstone slopes in the northern Jin-Shan Gorge of the Yellow River has induced widespread potential rockfalls, posing a significant threat to regional eco-environmental safety. This study aims to investigate the freeze-thaw damage characteristics and underlying mesoscopic mechanisms of the physical and mechanical properties of highly weathered mudstone in this area. A series of laboratory tests were conducted on natural moisture-content mudstone specimens under freeze-thaw cycles, including uniaxial compression tests, low-temperature nitrogen adsorption tests(NA), nuclear magnetic resonance(NMR)measurements, and scanning electron microscopy(SEM). The deterioration laws and mesoscopic mechanisms of mass, P-wave velocity, uniaxial compressive strength, and other physical-mechanical properties under freeze-thaw action were systematically examined. The results show that: (1)The mass, P-wave velocity, uniaxial compressive strength, and elastic modulus of the highly weathered mudstone exhibit more pronounced freeze-thaw degradation compared to other rock types, with total degradation rates after 30 freeze-thaw cycles reaching 4.7%, 10.2%, 59.7%, and 66.9%, respectively. (2)With increasing freeze-thaw cycles, the internal pore volume of the mudstone increases significantly. The nitrogen adsorption capacities after 0, 5, 10, 15, 20, 25, and 30 cycles are 13.767 mL·g^-1, 19.318 mL·g^-1, 19.693 mL·g^-1, 18.778 mL·g^-1, 20.083 mL·g^-1, 22.819 mL·g^-1, and 22.388 mL·g^-1, respectively. Concurrently, the surface meso-morphology evolves from relatively dense and smooth to loose and rough. (3)The freeze-thaw degradation characteristics of pores and morphology suggest that water-ice phase changes and resulting frost-heave pressure during freeze-thaw cycles promote the continuous expansion of pre-existing microcracks and generate a complex pore network dominated by small pores. This leads to a systematic increase in porosity and weakening of interparticle cementation, ultimately causing a sharp decline in the physical-mechanical performance of the mudstone. This study contributes to the fundamental understanding of freeze-thaw damage in mudstone and provides important insights for rock slope protection and ecological restoration in the Yellow River Jin-Shan Gorge region.