This research was carried out for evaluating diagnostic value of antibody test in Fragile X syndrome. In antibody test of control individuals and carriers with a premutation, FMRP were detected in the lymphocytes, whereas the lymphocytes of male Fragile X syndrome patients were devoid of FMRP. Five Fragile X syndrome male patient, two Fragile X syndrome female patients, three carriers were diagnosed by southern blot. Five boys who were diagnosed as the patients by antibody test were turned out full mutation and having multiple smear beside normal single band. However, fragile site of X chromosome was not expressed in Fragile X syndrome patients by chromosome analysis. These results showed that antibody test was a fast and simple method, but the diagnostic power was "perpect" for males, whereas the results were less specific for females.r females.