Leslie Julius Harris (1898-1973) was a British biochemist and nutritionist. He was Director of the Dunn Nutritional Laboratory (now the MRC Mitochondrial Biology Unit) in Cambridge, UK, from its foundation in 1927 until his retirement in 1963. He was instrumental in setting up the (British) Nutrition Society, and the International Union of Nutrition Societies. His research focused primarily on vitamins, including developing the for assessing vitamin C levels in a urine sample, and showing that vitamins A and D are harmful in excess.