Abstract: In August, 1996, 1000 adults of water hyacinth weevil, Neochetina eichhorniae, were released in an area of 1372 m² on a river totally covered by water hyacinth in Wenzhou, Zhejiang province. Two years after releasing only 25% of water hyacinth plants were controlled, but rapidly reached to 99% one year later. As most of the plants died in the releasing area, the weevils then dispersed into surrounding areas. In April, 1999, 70% of the water hyacinth in 3000 m² were controlled near the releasing site. By December, 1999, the weevils had moved to the area 20 kilometers away from the releasing site.