The author had tried to identify the sex from single tooth by detecting F-body of Y-chromosome in the nucleus of the dental pulp cells of 70 persons aged from 4 to 61 years under a fluorescent miscroscope. The results were as follows : 1. In the cell nuclei of male and female dental pulp at refrigeratory, the rate of F-body appearancd ranged 42-86%(average 61.06%) in male, while it was 0-6%(average 1.86%) in female, indicationg that male could be distinctly differentiated from female by F-body. 2. With male and female dental pulp puterfide by leaving in at room temperature, the rate of F-body appearance ranged 35-58%(average 48.20%) in male, 1-3%(average1.70%) in female, indicating that it was possible to distinguish male and female by F-body. 3. Even in heat-treated male teeth at $100^{circ}C$,10 mins, the rate of F-body appearace proved to be 32-56%(averaged 42.50%), also indicating the possibility of identifying male. 4. When detecting of F-body in process of time, the rate of F-body appearance did not show major charges. 5. It was reaffirmed that F-body detection method was a positive determination method of male.