The shortage of energy, especially fossil energy including coal, oil and gas, always is a world focus issue in which the world economic growth is influenced and limited strongly in developed countries and developing countries. The scarcity of freshwater and especially potable water is jeopardizing many regions of the world. Seawater desalination is a kind of technology gaining freshwater from seawater which need to consume a large amount of energy, so nuclear desalination technology is more and more important while the world oil price is over US$50 per boe and not down in recent years. Under the background of new world oil price, the economic competitiveness of seawater desalination projects between nuclear and fossil fuel was analyzed and presented, in which the power plant type include a pressurized light-water reactor (PWR), a pressurized heavy water reactor (PHWR), a superheated steam boiler using pulverized coal (PC), a combined cycle gas turbine (CC) and an open cycle gas turbine (GT), in a middle and large scale of about 600 MWe and 900 MWe, and coupled with the desalination technology: multi-stage flash (MSF). The calculation program is the desalination economic evaluation program (DEEP 2.1) developed by international atom energy agency (IAEA). The assumed sites of the seawater desalination plants studied are chosen to location in North Africa, Red Sea and South East Asia regions with similar seawater and economic conditions with respect to seawater desalination. The results based on the assumed site and economic conditions indicated: the averaged discounted water cost of nuclear options is economically visible compared to that of fossil fuel options. The four sensitive factors are used in the sensitive analysis: discount rate, fuel oil price, power plant investment and water plant size.