This project was planned for the east coast of Saudi Arabia and comprised 4 desalination plants, 2 power plants, 4 intake facilities and others. Mitsubishi Heavy Industries, Ltd. , undertook the construction of 2 desalination plants on the turn-key basis, from engineering works to installation and construction. 2 desalination plants consist of 20 evaporator units with 460,000 ton/day of water production and are ranked as the largest in the world. Details of civil and building works for these plants and the study on the important technical items are reported in this paper.