Abstract: To compare the effects of low calcium diet on bone in rats by bone histomor-phometry. Thirty-six 3-month-old Sprague-Dawley male and female rats （each half） were randomly divided into three groups, control group, very low calcium diet group （VLCD） and low calcium diet group （LCD）. After 90 days, all rats were killed. The proximal tibia （PTM） was harvested for histomorphometric analysis. The results revealed that the VLCD group male and female rats had lost 57% （P＜0.01） and 40% （P＜0.05） of cancellous bone compared with that of control group by 3 months respectively. Dynamic data in male and female rats showed that bone formation indices such as percent labeled perimeter（L. Pm%）,mineral apposition rate （MAR） and bone formation rate（BFR/BV） all increased without significance. Bone resorption indices such as osteoclast number per mm （Oc.N/Tb.Pm） increased 63% （P＜0.01）and 56% （P＜0.01）. The effect on LCD was lessen than in VLCD and there is significant bone loss only in male rats. The results indicated that bone loss was associated with increased bone turnover in low calcium dietary rats. The male rats were more sensitive to low calcium diet than female rats.

Key words: Low calcium diet, Osteoporosis, Bone histomorphometry