The vision disturbances of school-age children has been recognized as and important school health problem. The purpose of this study is to describe the current status of the visual health and to explore the related factors for the decrease in visual acuity in the elementary school age children. The study subjects were 697 children (Boys: 338, Girls: 359) of 4th to 6th grade in two school in urban area. The visual acuity data of the school health examination in 1999 and 2000 were utilized for analysis. The questionnaire for children and parents was used for survey. The findings were as follows. 1. The prevalance rate of the children with the visual acuity less than 0.7 on the left eye were 26.84％ ( Grade 4), 31.30％ (Grade 5), and 38.39％ (Grade 6). The rate on the right eye were 28.31％ (Grade4), 30.37％ (Grade 5), and 37.92％ (Grade 6). There was a significant difference in the rate of the visual acuity less than 0.7 according to grade (p<.01). 2.The rate of visual acuity decrease was 40.12％. 3. The factors related to the decrease in the visual acuity were grade, sex, genetic factor, posture, and the awareness of the visual acuity. There was more decrease in the visual acuity when the children were in higher grade (O.R= 1.06), girls (O.R=2.29). Children having parents with better vision (Father: O.R=1.26; Mother O.R= 1.25) showed better vision. On the other hand, when the children have siblings with glasses, there was more decrease in the visual acuity (O.R=2.31). Students with good posture during study (sitting on the chair) and watching TV to the lower direction showed less decrease in the visual acuity. Also, when the students know their visual acuity, the rate of decrease were lower. The variables which odds ratio were statistically significant were sex (p<.01), siblings with glasses (p <.01), and awareness of visual acuity (p<.01).