In an open letter to Oil Minister Ali al-Naimi and other ministers, published on Sunday via his Twitter account, Prince Alwaleed said demand for oil from OPEC member states was "in continuous decline".
He said Saudi Arabia's heavy dependence on oil was "a truth that has really become a source of worry for many", and that the world's biggest crude oil exporter should implement "swift measures" to diversify its economy.
Prince Alwaleed, owner of international investment firm Kingdom Holding, is unusually outspoken for a top Saudi businessman.
But his warning reflects growing concern in private among many Saudis about the long-term impact of shale technology, which is allowing the United States and Canada to tap unconventional oil deposits which they could not reach just a few years ago. Some analysts think this may push demand for Saudi oil, as well as global oil prices, down sharply over the next decade.