Medical Image Watermarking has been considered as an appropriate method for enhancing the data security and content verification in medical science. For the purpose of achieving better security it is recommended to hide the data in the medical image itself that will improve the reliability of medical information system. In our paper, the work is divided in two main stages, first of all image is divided into two parts: Region of Interest that is defined as informational part of image and Region of Non Interest that is defined as non-informational part. In our work we have used Region of Non Interest to hide the data so that the informational part of the image kept safe. Watermark is encrypted by using RSA. A Discrete Wavelet Transform based approach is used for embedding the encrypted data in Region of Non Interest part of image for enhancing data security. The experimental result shows that watermark embedded by the proposed algorithm provides better security and can survive successfully under different attacks.