Abstract: Objective To investigate the effect of genetic factor on the onset of myopia.Methods 4218 students in primary and middle school in Beijing were studied by questionnaire and eyesight examination by auto-refractometer.The SPSS 13.0 softw are and Falconer method were applied for the statistic analysis.Results There were 3064 students with simple myopia,the prevalence was 721.60%.There were 3283 with myopia,the prevalence was 77.80%.In the stutlents without myopia,the prevalences of myopia were 151.22% and 6.62% in the first-and second-degree relatives.In the students with simple myopia,the prevalences of myopia were 21.54% and 9.03% in the first-and second-degree relatives.In the students with myopia,the prevalences of myopia were 22.57% and 9.42% in the first-and seco nd-degree relatives.The Chisquare test showed that the prevalences of myopia in the first-and second-degree relatives were difierent(P=0.001).The heritabilities of simple myopia were 0.2804 and 0.3170 in the first-and second-degree relatives.The her itabilities of myopia were 0.3166 and 0.3631 in the first-and second-degree relatives.Conclusion Myopia is a polygenic disease.Genetic factors play some role in the pathogenesis of myopia,and also the environmental factors play an important role.