The official Xinhua News Agency said Saturday that 16-year-old Li Zhesi tested positive for a performance-enhancing drug EPO in March.
Li is one of the swimmers, who won gold in the 4x100m medley relay event at the worlds in Rome. Li also won 50-meter freestyle event at the 2010 Asian Games in Guangzhou.
EPO (short for erythropoietin) is a hormone that boosts the body's production of red blood cells, which carry oxygen — and more oxygen helps athletes perform better.
China has spent the past decade rebuilding its swimming program following a series of doping scandals that have devastated the sport in 1990s.