The changes in nuclecotides and their related compounds during the fermentation of Clam, Tapes japonica, were analyzed by high speed liquid chromatography. In raw Clam, dominant ADP was $7.86;{mu}mole/g$ on moisture and salt free base and the content of ATP was $3.85;{mu}mole/g$, AMP $3.71;{mu}mole/g$, hypoxanthine $0.28;{mu}mole/g$, inosine $0.15;{mu}mole/g$, respectively. But IMP was not detected in Clam ADP, ATP and AMP decreased while inosine and hypoxanthine incraesed by twenty two times and thirty there times respectively, after 63 days fermentation, when compared with raw samples. TMA- N increased while TMAO - N decreased during the fermentation The amount of TMAO nitrogen in 63 days fermented Clam was 66.0mg% on moisture and salt free base. It was belived that inosine, hypoxanthine and TMAO play an important role as flavour compounds in fermented Clam.