The hard clam (Meretrix lusoria) 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 of probiotics could increase the growth rate of hard clam. The aim of this work is to establish the characteristics of the hemogram and study the effects of seasonal variations, starving and feeding photosynthetic bacteria on hemogram of the cultured hard clam in Taiwan. This investigation is valuable in increasing understanding of the effect of the environment and probioiucs on the health of the hard clam. An annual change on hemograms due to seasonal variations was monitored monthly from February to October. Even though individual hemogram variation was found, after integrating 9 months of results and referring to the monthly record of environmental variations, no seasonal variation of the hemogram in relation to water temperature, salinity and pH was concluded. After starvation for 30 days, hard clams were found with hemocyte numbers lowered and proportions of SEGs reduced. Conversely, LEGs had increased markedly.