Ventilation in the scalded clam Tridacna（Flodacna）squamosa were examined by decreasing the oxygen partial pressure in the water. The ventilation volume increased from 571ml/min/kgWW （WW, the wet weight of soft part of the body） at oxygen saturated condition to 870ml/min/kgWW at 13.8 mmHg with decrease of oxygen partial pressure. The ventilation volume and the size of ctenidium were much smaller than those of the pearl oyster and the mussel. These results suggested that the scalded clam ventilates for the respiration rather than for the filtration.