Microwave irradiation has emerged as a promising technique for weakening high-strength rocks prior to excavation, with the potential to improve cutting efficiency and reduce mechanical energy consumption. In this study, we investigate the microwave-induced weakening behavior of two types of basalt—one from Vietnam and the other from Cheorwon, South Korea—under controlled laboratory conditions. Cylindrical rock specimens were exposed to 1000 W microwave energy for durations ranging from 1 to 10 min, and key physical and mechanical properties, including surface temperature, P-wave velocity, Schmidt rebound hardness, Leeb hardness, uniaxial compressive strength (UCS), and dry density, were measured before and after exposure. Results indicate that Cheorwon basalt is significantly more susceptible to microwave-induced weakening than Vietnamese basalt. Cheorwon basalt exhibited a UCS reduction of up to 20% after 5 min of exposure, a 28% decrease in Schmidt hardness, and a 10–12% decline in P-wave velocity, all of which point to internal microcrack propagation and surface degradation. Interestingly, the UCS of Cheorwon basalt partially recovered after 10 min of exposure, likely due to microcrack closure or stress redistribution at elevated temperatures. In contrast, Vietnamese basalt displayed only modest reductions in UCS and Schmidt hardness and only minimal changes in density or Leeb hardness. Dry density remained nearly unchanged in both rock types across all exposure durations, indicating that microwave damage is primarily microstructural and not volumetric. These findings demonstrate that microwave pretreatment can selectively and effectively weaken basalt without altering bulk geometry. The differential response between the two types of basalt highlights the influence of mineral composition and microstructure on microwave sensitivity. We conclude that microwave-assisted rock weakening offers a viable path toward more energy-efficient excavation in microwave-responsive lithologies.