The effects of newly developed sustained release recombinant bovine somatotropin(SR-rBST) on blood metabolites, concentration of blood BST, concentration of milk BST, health problems and reproductive characteristics of lactating dairy cows were examined. Forty eight holstein cows were randomly assigned to the four levels of non-treated control and SR-rBST treated groups(25㎎/d/head, 300㎎/14d/head, 500㎎/14d/head). The results obtained are summarized as follows: The SR-rBST treated cows showed increased levels of calcium, glucose, creatinine, urea in blood compared with control cows. Circular concentration of blood BST was significantly increased in the treated groups in comparison with control group. Circular concentration of milk BST was not different between the treated groups and the non-treated group. The health problems and reproductive characteristics were not affected by SR-rBST treatment. These results indicate that the newly developed SR-rBST administration to the dairy cow did not influence blood metabolites, concentration of milk BST, health probems and reproductive performances.