The possibility and effectiveness of cryopreservation was determined to assess survival rates and improve stock management of thawed embryos of Manila clam, Ruditapes philippinarum. The ideal freezing rates were designed and tested to allow cryoprotectants to equilibrate across the membrane during freezing. Survival rates ranging from 0 to 64.3% were obtained using a stepwise freezing protocol compared with 82.3% control rates. Embryos of Ruditapes philippinarum were equilibrated in 2 CPAs plus sea water for 10 min at 25°C and then cooled at -l°C/min from 20°C to -12°C. Straws containing more than 100 embryos were held at 12°C for 5 min allowing equilibration after seeding and slowly cooled at 2°C /min. to -35°C for 30 min for equilibration before quenching in liquid nitrogen. Dimethyl sulfoxide (DMSO) is the best cryoprotectant indicated for embryos of R. philippinarum with a survival rate of 64.3±3.28% in the presence of 2.0 M DMSO