Growth hormone (GH) is a single polypeptide hormone which is produced and secreted by cells of the anterior pituitary gland. This hormone exerts diverse Growth promoting and metabolic effects. As GH circulates in the blood, it binds to GH receptors (GHR), a trans membrane protein expressed on the surface of liver, adipose, kidney, heart, intestine, lung and muscle cells. After receptor binding, GH induces GHR dimerization and JAK2 is activated after its association with a dimerized GHR. A Growth hormone antagonist (GHA) was produced in E.coli by a mutation that would block GH by preventing the GHR dimerization. In this study, we evaluated the effect of mutagenesis on binding energy of GH and GHA to their related receptor. The Growth hormone and its mutant 3D structures were obtained from PDB (http://www.rcsb.org/pdb/home) and M4T server, respectively. Likewise, GHR conformational structure, was found in NCBI (http://www.ncbi.nlm.nih.gov). GH and GHA affinity for binding to GHR was analyzed by HEX docking software and energy total (E total) was obtained. GH and GHA E total were -648.13 and -698.68 respectively. This data demonstrates that GHA affinity for binding to GHR is higher than GH affinity. So GHA in completion to GH will overcome GH in binding to GHR, it can act as an antagonist to prevent excessive Growth and cure acromegaly, diabetes and cancer.