The present study aims to find out the main and interactional effect of defence mechanism and background variables locale (2), gender (2) on first dimension of self expression of high school students. The study was conducted on a sample of 300 high school students. Stratified purposive sampling technique was used to data collection. 2x2x2 factorial design was used to see the main and interactional effect. Locale, gender and defence mechanism were the independent variable whereas scores on self expression was the dependent variable. Defence mechanism Inventory developed by N.R.Mrinal and Uma Mrinal was used. This inventory consist 200 items. It measure five dimensions of defence mechanism and self expression Inventory developed by R.P Verma and Usha Mishra was used to measure two dimensions of self expression. The Result revealed that the three way interactional effect between locale*gender*defence mechanism on first dimension of self Expressions of high school students have not been found to be significant. On the basis of the result obtained the above hypotheses has been partially accepted.