This study investigates hardness and mass changes, sorption, and solubility of CAD/CAM resin composites reinforced with short fibers, woven fibers, or filler particles after storage in three buffer solutions for up to 60 days. Plate-shaped specimens were prepared from three resin composite blocks: the experimental short-fiber-reinforced composite (SFRC), TRINIA (TR), and Lava Ultimate (LU). For sorption and solubility measurements, specimens were immersed in three buffer solutions (pH 4, 7, and 10) for 60 days, weighed at intervals, then dried for a further 90 days at 37 ± 1 °C. Measurements included Vickers hardness and mass changes over 1, 7, 30, and 60 days of storage and SEM images. SFRC and LU were significantly harder than TR (p = 0.001). The average percentage hardness decrease after 60 days of immersion was comparable across the three materials (overall range: 26.8-32.88%), regardless of the acidity of the solution. SFRC showed minimal decreases in hardness and mass change across the study groups. The solubility range was between - 1.0 and 1.7 μg/mm. LU exhibited the highest sorption (p = 0.001). The experimental short fiber-reinforced composite (SFRC) exhibited relatively favorable outcomes more than the nanoceramic resin composite (LU) and greater stability than the woven fiber-reinforced composite (TR) after storage in aggressive acidic solutions over 60 days. The experimental short fiber-reinforced CAD/CAM resin composite exhibited relative mechanical stability among the studied materials and aging conditions. Generally, the studied materials were most greatly affected by alkaline storage compared to the other two buffer solutions.