The ocean is home to many large animals. What is the biggest? The Biggest Animal in the Ocean. The biggest animal in the ocean, and in the world, is the blue whale (Balaenoptera musculus), a sleek, light-colored giant. How Big is the Biggest Animal? Blue whales are thought to be the largest animal ever to live on the Earth. They reach lengths up to about 100 feet and weights of an amazing 100-150 tons. Blue whales are a type of baleen whale known as a rorqual. Despite their huge size, baleen whales like blue whales feed on small organisms.