The Le Day viaduct (viaduc du Day) is a railway viaduct in Vallorbe in the Jura-Nord vaudois District of the Swiss canton of Vaud. It stands near the hamlet of Le Day and crosses the Orbe. This has been dammed since 1955 by the Le Day dam (Le barrage du Day), which lies 450 m downstream.
The double-track bridge is used by TGV Lyria services between Paris and Lausanne on the Lausanne–Vallorbe line of the RER Vaud (Réseau express régional vaudois) and the line from Vallorbe to Le Pont in the Vallée de Joux with its extension to Le Brassus.