Vasily Iakovlevich Danilewsky (variously spelled Vasili Yakovlevich Danilewsky or Vasili Yakolevich Danilevski or Vasily Yakovlevich Danilevsky, Russian: ??????´????? ????´??? ?´????????) (13 or 25 January 1852 – 25 February 1939) was a Ukrainian-born Russian physician, physiologist and parasitologist.
He was professor of physiology at University of Kharkiv and then at Kharkiv Medical Institute.
He helped to establish the Danilevsky Institute of Endocrine Pathology Problems which he directed until his death.
Danilewsky made important works in physiology, particularly in neurobiology.
He was the first to give comprehensive description of nerve impulse in the brain of dogs.
He also worked on the physiological responses of hypnosis in animals and humans.
He was one of the pioneers in study of insulin action.
However his most well known contribution is in parasitology.
He was the first to investigate systematically on blood parasites of vertebrates such as birds, reptiles, and amphibians.
He is the binomial authority of a number of bird parasites.
His paper titled "About Blood Parasites (Haematozoa)" published in 1884 in the Russian Medicine journal is regarded as the foundation of modern parasitology in bird malaria and other protozoan infections.
A species of blood parasite in bird Haemoproteus danilewskyi is named after him.