The study was aimed to investigate the changes in carcass traits, meat quality, muscle fiber characteristics, and liver function in pigs fed with high levels of fresh fish oil and oxidized fish oil. About 30 piglets were randomly assigned to receive basal diet plus 2% fish oil (LFO), basal diet plus 8% fish oil (HFO), or basal diet plus 8% oxidized fish oil (OFO) for 120 d. Pigs of the HFO and OFO group showed reduced carcass weight, dressing percentage, loin eye area, and increased yellowness of the longissimus dorsi muscle compared with LFO group (P < 0.05). Dietary HFO and OFO suppressed the relative expression levels of myosin heavy chain (MyHC) isoform (I and II a), glutathione peroxidase 4, and NAD(P)H: quinone oxidoreductase-1 and mitochondrial biogenesis in longissimus dorsi muscle (P < 0.05). Dietary HFO or OFO increased the serum aspartates aminotransferase, alanine aminotransferase, total bilirubin, direct bilirubin, oxidized low-density lipoprotein, liver index, and concentration of malondialdehyde (MDA) in liver (P < 0.05). In conclusion, high levels of fresh fish oil and oxidized fish oil have adverse effects on carcass traits, muscle fiber characteristics, and liver function, which may be partly due to the mitochondrial dysfunction and impaired antioxidative capacity.