Oyster (Crassostrea gigas) culture has been operating on the west coast of Taiwan for two hundred years. In recent years, the occurrence of shell chambering in oysters was noticed, but lack of scientific studies. This study concentrated on: 1. Evaluation of shell chambering methods. 2. Possible relationship between chambering and Thais clavigera predation. 3. Relationships between chambering and heavy metals. The results suggested that shell thickness index (STI) and density reflect chambering status adequately. There was a negative trend between depth of drilling hole by T. clavigera and density of oyster shell, but not significantly. Amount of total heavy metals did not appear significantly related to shell chambering neither.