Abstract: This paper presents the transmission technique, which has been designed and developed for the study of water core in apple cultivars Red Delicious and Golden Delicious of Himachal Pradesh, India. The principle of this method is to measure the optical density of the sample at 2 selected wavelengths and computation of the optical density difference. It has been observed that Golden Delicious is more prone to water core than Red Delicious. The technique is simple and can be conveniently implemented to develop an on-line instrument to monitor water core in apples.