Giant clams (Tridacnidae) are economic species which have been the main materials for ganbei. Due to a huge decline in population size, it was reported as an endangered species in CITES list. In this study, the effects of different preservative methods on the expression of DNA sequences in giant clams were examined and whether ganbai is made from giant clams were also determined. I collected samples from Kenting, Green Island, Orchid Island, Shaio-Liu-Chu and Penghu Islands. And, ganbei were bought from markets. Species identification was based on four DNA sequences (COI, 16S, 18S, 28S) and morphological characters. The distinction power of four preservative methods (-70 ¢J frozen, 70 % ethanol, dried and freeze dried) on clam samples was evaluated. DNA sequences of CO1 and 16S are the best fragments to distinguish samples at species level. Additionally, a cryptic species of Tridacna noae was found from Tridacna maxima. The 18S and 28S sequences have low variation among giant clam species which are more suitable for higher level of phylogeny. The DNA fragments with different preservative methods were mostly in good condition having extracted DNA size up to 10 Kb. The sequencing divergences of the four preservation were 0 - 0.020 within an individual and 0 - 0.070 among individuals. In conclusion, the four preservative methods are similar in sequence expression. Ganbei made from giant clams was not found in the market. Instead, commercial ganbei are made from scallops, mostly Patinopecten yessoensis and some Argopecten irradians.