PurposeTo estimate the prevalence of myopia among primary and middle school-aged students in Guangzhou and to explore the potentially contributing factors to myopia.MethodsThis cross-sectional study was based on a sample of students in grades 1-6 and grades 7-9. Data were collected from refractive error measurements and a structured questionnaire.ResultsA total of 3055 participants were involved in this analysis, and the overall prevalence of myopia was 47.4% (95% confidence interval (CI)= 45.6-49.2%). The prevalence of myopia in students increased along with the growth of grade level; the prevalence of myopia in students in grade 1 was only 0.2%, as it increased to 38.8% in students in grade 3, and the rate was the highest (68.4%) in students in grade 9. Girls were at a higher risk of myopia than boys (adjusted odds ratio=1.22, 95% CI=1.04-1.44). Both male and female students whose distance of reading was longer than 25 cm were less likely to have myopia and who have one or two myopic parents were at a higher risk of myopia. In addition, reading for pleasure more than 2 h per day (adjusted odds ratio=1.84, 95% CI=1.09-3.12) was only positively associated with myopia in boys and spending time watching television per week was only positively associated with myopia in girls.ConclusionMyopia in students is a significant public health problem in Guangzhou. Female gender, higher grade, longer time spent for near work, shorter distance of near work, and parental myopia were shown to be associated with the increasing risk of myopia in children.