We reviewed the research report with regard to mental deficiency that published in Ja pan and Europe & America in 1963-1968. Contents of that review were the following sections of the research on Mental Deficiency. l ) Electroencephalogra phy 2) Personality Theory & its Experimental Research 3) Learning 4) Psychotherapy 5) Therapeutic Education 6) Speech Disorder On personality theory and its experimental research,'we reviewed chiefly studies in Europe & America and on therapeutic education, we reviewed chiefly studies in Japan.