Charles L'Eplattenier (1874–1946) was a Swiss painter and architect.
A contemporary and associate of René Chapallaz, Léon Gallet, and Le Corbusier, L'Eplattenier is considered one of the foremost exponents of Swiss Art Nouveau despite working almost exclusively in the town of La Chaux de Fonds, where from 1897 he taught at the school of decorative arts. He taught the architect Le Corbusier. It is possible that Le Corbusier was influenced in his choice of pseudonym by the name of his teacher.
At the time La Chaux-de-Fonds was developing into one of the leading centres of the Swiss watch industry. Increasing prosperity created a large demand for property and art in the style of the time among the wealthy citizens of the city. L'Eplattenier and his students developed a local form of Art Nouveau known as style sapin ("pine style") after a frequently recurring motif. Style sapin is characterised by an intensive study of nature and the artistic stylization of indigenous structures.
L'Eplattenier's works include monuments to the Republic and the politician Numa Droz in La Chaux-de-Fonds, figures and decorative elements in the town's crematorium and at the cemetery, as well as repoussé and enamel watch case designs for the Gallet Watch Company. Upon funding for construction at the bequeath of Léon Gallet, the Musée des beaux-arts de La Chaux-de-Fonds (Beaux Arts Museum of La-Chaux-de-Fonds), was built to L'Eplattenier's designs.
L'Eplattenier also designed a prototype military helmet designed, which was shunned in favour of the Imboden helmet. They are now prized collectors' items.
A lover of the outdoors, L'Eplattenier fell to his death from one of the rocky promonitories while hiking along the River Doubs, near Brenets, Switzerland.