This study was carried out to investigate the effects of fermented mushroom (Flammulina velutipes) by-products on meat quality characteristics in fattening Berkshire pigs. The fermented diet mainly contained 40.0% mushroom by-products, 26.0% rice bran, and 20.0% formula feed and was fermented for 5 d. The basal diet for the control (C) was substituted with 10% (T1), 30% (T2), 50% (T3), and 70% (T4) fermented diet. Warner-Bratzler shear forces (WBSF) were significantly lower (P < 0.05) in treatments than that in C. The meat color (lightness, redness, and yellowness) was significantly lower (P < 0.05) in treatments than that in C, whereas fat color (redness and yellowness) was significantly higher in treatments than that in C (P < 0.05). The compositions of palmitoleic acid and arachidonic acid were significantly higher (P < 0.05) in T4 than that in C. The amino acid composition of longissimus dorsi (LD) and the sensory evaluation of cooked meat were not affected by diet type. In conclusion, a diet of fermented mushroom by-products increased pH and backfat color, but decreased cooking loss, WBSF, and meat color of LD in growing-fattening Berkshire pigs.