Gastilonys is a former village in the Kaišiadorys District Municipality, Lithuania, located 1 kilometer south of Grabučiškės, on the right bank of the Kaunas Reservoir.

The Gastilonys Botanical-Zoological Reserve has been established in the village, where Gastilonys oak [lt] grows.

The village used to be on the right bank of the Neman, east of Mozūrai [lt].

In 1959, Kaunas was flooded during the construction of the Kaunas Hydroelectric Power Plant, creating the Kaunas Reservoir.

The name of the village comes from the surname Gastila.