The main purpose of this research is to find the prevalence of mentally retarded students in Public Junior High Schools. The number of subjects is 1,000 with 596 boys and 404 girls. They are inhabitants of the northern, middle, and southern part of Taiwan. 　　The Revision of AGCT for the Chinese people was selected as an instrument to measure the students' IQ. 　　The testing results have been carefully analysed and indicate 4.30% as the percentage of mentally retarded students in Public Junior High School. The statistical data of test scores suggested that there is no sex difference in the prevalence, and the geographic variations are negligible.