The effect of low calcium (LC) diet supplemented with various amount of calcium on serum calcium and calmodulin of rats was studied. The LC diet was mainly composed of corn low in calcium. The calcium content of LC diet was only half of that of the stock diet. Seventy Wistar rats were divided into 7 groups by weight and sex. Results showed that serum calcium in LC group was low and calmodulin activity was also low. These parameters were improved while calcium was supplemented in LC diet. There is a significant dose-response relationship among diet calcium, serum calcium and growth. When the total calcium in diet was increased up to 1000 mg/kg, serum calcium level was closed to that of normal and higher than the serum calcium in LC group significantly. The study demonstrated that low dietary calcium, hypocalcemia and low calmodulin are associated. When total dietary calcium was up to 1000 mg/kg, the growth retardation was attenuated.