Propyl alcohol and butyl alcohol had similar effects to ethyl alcohol on ultrastructure of liver mitochondria. Rats were given 32% ethyl alcohol, 32% n‐propyl alcohol, and 6.9% n‐butyl alcohol in drinking water for up to three months. After one month, mitochondria in hepatocytes obtained from the experimental animals became elongated, constricted or cup‐shaped with scanty cristae. After two months, mitochondria in some hepatocytes became gigantic. In extreme cases, the megamitochondria exceeded 10 μm in diameter.Coupling efficiencies of hepatic mitochondria obtained from alcohol‐fed animals were well preserved despite their drastic morphologic changes. ACTA PATHOL. JPN. 34: 471–480, 1984.