So many studies on the sex chromatin have been made so far in various fields since it was discovered as a nucleolar satellite by Barr and Bertram in 1949, but very little has been described about the sex chromatin in exfoliated cells of oral neoplasms. Thus the author started this investgation of the sex chromatin in oral smears in 60 normal persons (30 males and 30 females), 35 benign tumors (17 males and 18 females), 35 malignant tumors (22 males and 13 females) and 14 sexual anomalies. All smear specimens were stained with Moore and Barr's cresyl echt violet technigue, and a sex chromatin was always located along the inner surface of the nuclear membrane of interphase nuclei. The results obtained were as follows; 1) NORMAL CASES Microscopic examination was made on the sex chromatin in smear specimens taken from buccal, gingival and lingual epithelia of the same individual. Incidence of the sex chromatin in females was on an average 23.5±6.50 per cent in buccal smears, 22.0±5.65 per cent in gingival and 21.6±5.76 per cent in lingual, while that in males was ranging from 0 to 2 per cent in smears taken from each area. Minute examinations of sex chromatin showed that they were noticed in a variety of forms, such as triangular, planoconvex, flat and others, of which triangular form was most commonly seen. The average size of sex chromatin in these epithelial cells was about 1.4 X 1.0 μ. 2) TUMOR CASES There was almost no difference between sex chromatin incidences of tumor and its host tissue, except two cases of benign neoplasam, i. e. fibroma and follicular cyst, in females, whose sex chromatin incidences were 4 and 6 per cent. A relationship between sex chromatin incidence and Broders' classification could not be noticed in cases of carcinoma cells. 3) INTERSEX AND SEXUAL ANOMALIES As the result of investigations of sex chromatin in cases of pseudohermaphrotidism, infantilism, Turner's syndrome and hypospadias, the sex chromatin pattern did not always agree with its genetic sex in the patients associated with sex chromosome aberrations, therefore, it will be desirable to make analysis of sex chromosome in determining the sex in the above mentioned patients.