Ergocalciferol, also known as vitamin D₂ and nonspecifically calciferol, is a type of vitamin D found in food and used as a dietary supplement. As a supplement it is used to prevent and treat vitamin D deficiency. This includes vitamin D deficiency due to poor absorption by the intestines or liver disease. It may also be used for low blood calcium due to hypoparathyroidism. It is used by mouth or injection into a muscle.

Excessive doses can result in increased urine production, high blood pressure, kidney stones, kidney failure, weakness, and constipation. If high doses are taken for a long period of time, tissue calcification may occur. Normal doses are safe in pregnancy. It works by increasing the amount of calcium absorbed by the intestines and kidneys. Food in which it is found include some mushrooms.

Ergocalciferol was first described in 1936. Ergocalciferol is available as a generic medication and over the counter. In 2020, it was the 46th most commonly prescribed medication in the United States, with more than 14 million prescriptions. Certain foods such as breakfast cereal and margarine have ergocalciferol added to them in some countries. It is on the World Health Organization's List of Essential Medicines.