As amino acids take an important role in biology, it is envisaged that understanding of their interactions with nanomaterials can resolve critical problems in the field of biomedicine. Graphene, single atom thick hexagonal lattice of sp(2)-bonded carbon, can be used for this purpose. The remarkable properties of graphene sheets could facilitate their application in areas like hydrogen technology, electronics, and sensing. In this work, we report density functional theory calculations of the adsorption of Histidine and Leucine molecules on pristine and decorated (Ti,C and O) graphene. The obtained binding energies of molecules on graphene surface are in good agreement previous studies. The chemisorption is achieved when Graphene is decorated with Ti and C. It is also shown that how modify structural properties of the molecules on pristine (Graphene by applied charging for the first time.