Émile Duclaux (24 June 1840 – May 2, 1904) was a French microbiologist and chemist born in Aurillac, Cantal.
He studied at the College of Aurillac, the Lycée Saint-Louis in Paris and at École Normale Supérieure. In 1862 he began work as an assistant in the laboratory of Louis Pasteur (1822–1895). During his career, he taught classes in Tours (1865), Clermont-Ferrand (1866), Lyon (from 1873) and Paris (from 1878). In Paris, he was a professor of meteorology at the Institute of Agronomy. For much of his career he was associated with the work of Louis Pasteur.
In 1888 he was elected to the Académie des sciences, and in 1894 became a member of the Académie Nationale de Médecine.
Duclaux's work was largely in the fields of chemistry, bacteriology, hygiene and agriculture. Duclaux initiated the custom of naming enzymes by adding the suffix "-ase" to the enzyme's substrate. His intention was to honor the first scientists (namely Anselme Payen, 1795–1871; and Jean François Persoz, 1805–1868) to isolate an enzyme; "diastase", in 1833. With Pasteur, he collaborated in the study of silkworm diseases, and also took part in experiments to debunk the theory of spontaneous generation. In the 1870s, he undertook studies of phylloxera, an aphid-like pest that plagued grape vineyards. In addition, he performed research on the composition of milk, and conducted studies on beer and wine.