Abstract: Morphologically, two species of giant clams Tridacna have been recognized in the Red Sea, T. squamosa and T. maxima. Similar morphology among species makes classification difficult. For proper classification, we sequenced an approximately 450-nucleotide fragment of the mitochondrial 16S rDNA gene from the tissues of Tridacna from eight locations in the Red Sea. Our results suggest that there are three novel species of Tridacna in the Red Sea. Two of these species are related to T. maxima and one is related to T. squamosa. Of the two species related to T. maxima, one species was found in Hurghada, Marsa Ghaleb and Safaga while the other was found in Abu Zenima, Abou Galum, Dahab and Nuweiba. All three novel species were found in Ras Mohamed. Our results do not support the morphological classification that suggests the existence of only two tridacnid species, T. maxima and T. squamosa in the Red Sea.