The hard clam (Meretrix spp.) is a common and important bivalve species, cultivated along the southwest coast of the island of Taiwan. However, the hard clam has suffered high mortality each spring and summer since 1969 . Possible causes have been suggested, such fluctuating temperature, sudden change of salinity after heavy rainfall, industrial pollution, pesticide pollution and infectious shellfish diseases, but the exact cause remains unknown. However, many reports shows that applicaion in farm of probiotics could increase the growth rate of hard clam. The aim of this work is to study the effects of photosynthetic bacteria on Immunological parameters , inculding hemograms, neutral red uptake assay, phagocytosis assay and reactive oxygen species produuction in the cultured hard clam in Taiwan. This investigation is valuable in increasing understanding the benifits of probiotics applying in the health of the hard clam.