: The aim of the study is to determine the sex of the skull with Mastoid process and also to derive discriminant analysis formula for south Indian skulls. 70 adults skulls (38 male & 37 female) from Department of Anatomy, SRM Medical College is utilized for the study. The Mastoid length, anteroposterior diameter, Mediolateral diameter, surface was studied to calculate the size of the mastoid process. The measurement is recorded, tabulated andanalysedusing SPSS-14software. Univariate Analysis (Mean, Standard deviation & P Value), Student t test (to Discriminate Male and female) and Discriminant Function test was done to arrive the discriminant function formula and logistic regression to discriminate the sex of the mastoid (Wilks lamba, Eigen Value, Canonical Correlation, % of correct class. Mean values of mastoid length, Medio lateral diameter, anteroposterior diameter and surface area is high in males when compared to females. All four variables showed significant P – value. All four Bony variables correctly grouped male and female mastoid process to accuracy of 97.1% in Step wise analysis which was statistically significant. Left mastoid Surface is the good predictor of whether the skull belongs to male or female Discriminat Function D1 = 1 * (Left Mastoid Surface Area). Group Centroid: Male 0.485 (> -0.045), Female -0.576 (< - 0.045), Cut Score -0.045. All the four mastoid variables (Length, ML, AP & Surface Area) are good predictor for sex determination. The external efficacy of the study was checked by logistic regression which is robust against violation of normality and homoscedastictiy. Discriminant function equation had been derived for the south Indian population..