Bovine somatotropin (bST) is a protein growth hormone secreted from anterior pituitary gland in response to growth hormone releasing factor. Somatotropin has the potential to increase the efficiency of milk production in cows by 10-15 percent with less than 5 percent on feed intake. On November, 1993, the FDA announced approval of a bST product for increasing milk production in dairy cows. Recombinant bovine somatotropin (rbST) is the first biotechnology product has been widely used to improve milk production in cows to meet the growing needs of nutrition. The authors cloned and expressed bST in E. coli JM109 (DE3). In this report rbST has been expressed and refolded in biologically active form. The inclusion body was solubilized by 8 M urea, and purified through NTA column and Supedex 75. The circular dichroism spectrum of recombinant bST and native bST is similar. The soluble rbST was analyzed for biological activity by Nb2 lymphoma cell. It was found that the rbST had biological activity.