The Sumatran tiger is a population of Panthera tigris sondaica on the Indonesian island of Sumatra. It is the only surviving tiger population in the Sunda Islands, as the other Bali and Javan tigers went extinct during the 20th century.

Sequences from complete mitochondrial genes of 34 tigers support the hypothesis that Sumatran tigers are diagnostically distinct from existing mainland subspecies. In 2017, the Cat Classification Task Force of the Cat Specialist Group revised felid taxonomy and recognizes the living and extinct tiger populations in Indonesia as P. t. sondaica.

Felis tigris sondaicus was the scientific name proposed by Coenraad Jacob Temminck in 1844 for a tiger specimen from Java.

Panthera tigris sumatrae was proposed by Reginald Innes Pocock in 1929, who described a skin and a skull of a tiger zoological specimen from Sumatra. The skull and pelage pattern of tiger specimens from Java and Sumatra do not differ significantly. P. t. sondaica is therefore considered the valid name for the living and extinct tiger populations in Indonesia.

Analysis of DNA is consistent with the hypothesis that Sumatran tigers became isolated from other tiger populations after a rise in sea level that occurred at the Pleistocene to Holocene transition about 12,000–6,000 years ago. In agreement with this evolutionary history, the Sumatran tiger is genetically isolated from all living mainland tigers, which form a distinct group closely related to each other. The isolation of the Sumatran tiger from mainland tiger populations is supported by multiple unique characters, including two diagnostic mitochondrial DNA nucleotide sites, ten mitochondrial DNA haplotypes and 11 out of 108 unique microsatellite alleles. The relatively high genetic variability and the phylogenetic distinctiveness of the Sumatran tiger indicates that the gene flow between island and mainland populations was highly restricted.

The Sumatran tiger was described based on two zoological specimens that differed in skull size and striping pattern from Bengal and Javan tiger specimens. It is darker in fur colour and has broader stripes than the Javan tiger. Stripes tend to dissolve into spots near their ends, and on the back, flanks and hind legs are lines of small, dark spots between the regular stripes. The frequency of stripes is higher than in other subspecies. Males have a prominent ruff, which is especially marked in the Sumatran tiger.

The Sumatran tiger is one of the smallest tigers. Males measure between the pegs 2.2 to 2.55 m (7 ft 3 in to 8 ft 4 in) in head-to-body length, with the greatest skull length of 295 to 335 mm (11.6 to 13.2 in) and weigh 100 to 140 kg (220 to 310 lb). Females weigh 75 to 110 kg (165 to 243 lb) and measure 2.15 to 2.30 m (7 ft 1 in to 7 ft 7 in) in length between the pegs with a greatest length of skull of 263 to 294 mm (10.4 to 11.6 in).

A near telomere-to-telomere chromosome-level genome assembly of the Sumatran tiger was published in 2026; the genome is approximately 2.46 Gb in size, spans 19 chromosomes, has a BUSCO completeness of 95.3%, and 23,737 protein-coding genes were predicted.