Aim: to study the prevalence of refractive error of school children at Hanoi. Methods: cross - sectional and prospective study in 2009. The study carry out on 6.184 children (3.222 males, 2.962 females) from primary and secondary schools, of 4 districts in Hanoi, aged 7 -15 years. Results: the prevalence of myopia (SE at least - 0.750): 33,7 percent. The rate of myopia in female children (35.0 percent) were than male children (32.5 percent), (p 0.05). The rate of myopia in Ba Dinh district (42.3 percent), Thanh Xuan district (41.0 percent) and Tu Liem (44.3 percent) were higher than the Dong Anh district (18.8 percent), (p0.001).