Sailly-sur-la-Lys (French pronunciation: [saji syʁ la lis], literally Sailly on the Lys; West Flemish: Zelleken) is a commune in the Pas-de-Calais department in the Hauts-de-France region of France.

[3] Sailly-sur-la-Lys is a large farming and light industrial village situated some 9 miles (14 km) northeast of Béthune and 12 miles (19 km) west northwest of Lille, at the junction of the D945 and D66 roads.

The river Lys forms much of the western and northern boundary of the commune.

The gateway, which was destroyed in the sixteenth century and rebuilt in 1612, is defended by two towers with mullioned windows.

Before the French Revolution, it was the provost that represented the abbot of Saint-Vaast in all matters civil and judicial.