The purpose of this study was to determine the quantity of relapse in the intercanine and intermolar widths that occur in one hour time in the rapid palatal expansion applied cases where the appliance used is planned to be used for retention right after the completion of the R.P.E. procedure. The study consisted of 23 individuals including 16 girls and 7 boys at a mean age of 12.55 years. The statistical significance of the post expansion and after one hour time values were evaluated using paired t test. In conclusion, the relapse that occurred within one hour time was found to be statistically significant and it was observed that the decrease in the intermolar width was greater than that in the intercanine width. The result of this study suggests that preventive measures must be taken in order to avoid relapse after the completion of R.P.E. procedure.