Kostilka Island (, ) is the rocky island 213 m long in westâÂÂeast direction and 137 m wide in the Myriad Islands group of Wilhelm Archipelago in the Antarctic Peninsula region. Its surface area is 1.64 ha.
The feature is so named because of its shape supposedly resembling a fruit's stone ('kostilka' in Bulgarian), and in association with other descriptive names of islands in the area.
Kostilka Island is located at , which is 3.35 km northwest of Flank Island, 3.47 km southeast of Final Island, and 6.74 km west-northwest of Vedel Islands. British mapping in 2001.