In this presentation, the oyster shell was considered as a treatment material to reduce the phosphorus load in the farmland drainage channels. Oyster shell used was applied to the field after washing process only without artificial treatment processes, i.e. heat treatment & grinding etc. Acrylic container box was manufactured to install the oyster shell in the treatment zone of the drainage channel. Various monitoring works were carried out to investigate the efficiency of oyster shell with time. As a result of monitoring, about 15 % of phosphorus reduction was observed.