A considerable number of papers have been published in the last decade about biometric recognition using palm-print features. One of the most important stages in these methods is pre-processing which contains some operations such as filtering, Region Of Interest (ROI) extraction, normalization, etc. This paper proposes a precise method for extracting ROI of the palm-print. The basis of this method is geometrical calculations and Euclidean distance. Although preprocessing has been discussed in different papers incidentally, but no definite precise approach has been introduced. We show that our approach will extract the ROI with the accuracy of 99.7%