Xiaohui Fan (born 9 December 1971 in Beijing, China) is an American astronomer, and full professor at University of Arizona. He is widely known for his studies on quasars, extremely bright supermassive black holes, detected primarily at high redshift. In 2003, Fan was named to Popular Science magazine's annual Brilliant Ten list for developing methods to investigate distant quasars. Since 2001, he was a pioneer in the detection and discovery of high-redshift quasars, introducing new techniques and practically inventing the field. Using these quasars, he has shown that supermassive black holes with masses up to 10 million solar masses existed within one billion years after the big bang. In 2019, he led an international team of astronomers that discovered the farthest lensed quasar thus far,