Blakiston's Fish Owl, Bubo blakistoni, is an owl. This species is a part of the family known as typical owls, Strigidae, which contains most species of owl. Blakiston's Fish Owl and three related species were previously placed in the genus Ketupa; mtDNA cytochrome b sequence data is equivocal on which genus name is applied for this species (Olsen et al. 2002). Its habitat is riparian forest, with large, old trees for nest-sites, near lakes, rivers, springs and shoals which don't freeze in winter.

It feeds on a variety of aquatic prey, including fish and amphibians, but also takes small mammals and birds to the size of hazel grouse (Slaght and Surmach 2008). It also takes carrion, as evidenced by fish owls in Russia being trapped in snares set for furbearing mammals, which use raw meat as bait.

Blakiston's Fish Owl is a massive owl at 60-75cm (24-30 in) and is possibly the largest species of owl. A recent field study of the species showed males weighing from 3 to 3.75 kg (6.6-8.3 lbs), with the female, at up to 4.5 kg (10 lbs), being about 25% larger. Superficially, this owl looks like the Eurasian eagle owl, but is paler, and has broad, ragged ear tufts. The upperparts are buff-brown and heavily streaked. The underparts are pale buffish-brown. The throat is white. The iris is yellow (whereas Eurasian eagle owl has an orange iris). Vocalizations differ among the two recognized subspecies. In the island subspeies, the male calls twice and the female responds with one note, whereas the mainland subspecies has a somewhat more elaborate, 4-note duet:"HOO-hoo, HOOO-hoooo" (here, the male call is in capital letters (HOO) and the female call in lower case (hoo)). This duet is so synchronized that those unfamiliar with the call often think it is only one bird calling. When an individual bird calls, it sounds like hoo-hooo. Juveniles have a characteristic shriek.

This bird is endangered due to the widespread loss of riverine forest, increasing development along rivers and dam construction. The current population in Japan is approximately 100-150 birds (20 breeding pairs and unpaired individuals), whereas on mainland Asia the population is much higher, perhaps several thousand individuals (Slaght and Surmach 2008).

Henry Seebohm named this bird after the English naturalist Thomas Blakiston, who collected the original specimen in Hakodate on Hokkaid?, Japan in 1883.