Parathyroid hormone has clearly emerged as the most promising new anabolic treatment for osteoporosis by increasing the activation of osteoblast. It is known that chlorella increases both bone mineral density (BMD) and the rate of bone formation. The purpose of the present study was to determine whether the chlorella dietary supplementation could effect the thyroid or parathyroid hormones associated with increased BMD and bone formation. Twenty-two postmenopausal woman were treated for four month with 4 gm of chlorella dietary supplementation per day, then assessed serum calcium,25 OH vitamin D$_3$, thyroid hormone and parathyroid hormone before and after treatment. The mean 25 OH vitamin D$_3$ and parathyroid hormone were shown to marked increases by 193% and 265% respectively, in contrast to decreases by 9.4%, 37%, 33% and 14% in serum calcium, triiodo-thyroxine, free thyroxine and thyroxine stimulation hormone. In conclusion, treatment of postmenopausal women with chlorella dietary supplementation resulted in an increase in BMD and bone formation through enhancement of parathyroid hormone and 25 OH vitamin D$_3$, and a decrease in thyroid hormones.