Khong Island or Don Khong is the main island of the Si Phan Don riverine archipelago located in the Mekong River, Khong district, Champasak Province, southern Laos.

The island is 18 kilometres (11 mi) long (north-south), and 8 kilometres (5.0 mi) at its widest point. It has a population of approximately 55,000, mainly concentrated in the two villages Muang Saen (west) and Muang Khong (east); the latter is considered the de facto capital of the island. The former President of Laos, Khamtai Siphandon has a residence on the island, and explains the surprisingly high-quality of infrastructure, such as asphalted roads and electricity, on the island. Locals tend to travel on longtail boats.

The Khong island is noted for its natural beauty and is a growing tourist destination. Many tourists combine their visit to the island with a visit to the nearby Don Det and Don Khon islands, where it is easier to view the Khone Phapheng Falls.

It is near the Cambodian border.