Despite the harsh environment of the Kuril Islands, many animal and plant species inhabit the archipelago. All biotic communities arrived from the areas of present-day Japan, in the south, and Russia, in the north. Most colonization events took place between the end of the Last Glacial Maximum and the early Holocene (~22,000 – 10,000 years ago). Between 18,000 and 15,000 years BP, the sea level was 426 feet (130 m) lower than today. Many of the southern islands were connected to the Japan mainland, while Paramushir and Shumshu islands, in the north, were connected to the Kamchatka.

The flora of the Kuril Islands consists of 1,194 species. The geographic distribution of plants primarily relates to latitude and altitude. Overall, habitat diversity declines with increasing latitude due to decreasing mean temperatures and length of growing season In addition, ocean currents also affect plant distributions. While warm ocean currents are present on the Sea of Okhotsk side, cool currents hinder growth on the Pacific Ocean side.

The southern Kuril Islands consist of a diverse range of vegetation. Broadleaf forests composed of oak, white elm, and birch; boreal coniferous forests consisting of fir and spruce; grasslands with shrubs; and wetlands with swamps are found throughout the southern islands. In contrast, only shrub thickets and herbs, best characterized as tundra, dominate the vegetation of the central and northern islands.

The fauna of the Kuril Islands exhibits a similar distribution pattern. Although the Kuril Islands are inhabited or visited by over 170 bird species, the southern islands are home to the greatest diversity of birds, where falcons, eagles, puffins are present. As of the mid-20th century, only a handful of terrestrial mammals were reported in the southern islands, including fox, bear, and river otter. Bear, shrew, voles, and weasel are reported on two northern islands. Fox, which can survive on variety of food such as shellfish, bird eggs, fish, and vole are the only widespread terrestrial mammals known today in the central Kuril Islands.

The maritime environment also supports a number of freshwater and marine fish and marine mammals. Sea otter, harbor seals, northern fur seal, and sea lion inhabit the shores and bays throughout the islands. Fish species in archipelago include char, salmon, herring, cod, and Atka mackerel. Common shellfish are mollusks, mussels, clams, and sea urchins.