In this study the density theory (DFT ) Ab initio quantum chemistry methods and Gaussian 09) program were applied to the calculation of the balanced geometry (bond lengths, length angles in Angstrom) of acyclovir (2-amino-9-(2- hydroxyethoxymethyl)-1H-purin-6-one Some its Derivatives Methylacyclovi (2- Amino-9-[(2-hydroxyethoxy)methyl]-1-methyl-1,9-dihydro-6H-purin-6-one ) and Ganciclovir (2-amino-9-(((1,3-dihydroxypropan-2-yl)oxy)methyl)-1,9-dihydro-6H-purin-6- one) .The thermodynamic functions ( E0 , H0 ,A0 ,S0 ,CV ) was calculated of compounds studied and also some physical properties (EHOMO,ELUMO , ∆E , IP ) was also calculated . The research paper concluded that the (2-amino-9-(((1,3- dihydroxypropan-2-yl)oxy)methyl)-1,9-dihydro-6H-purin-6-one) ganciclovir compound has the larger HOMO-LUMO gap and larger thermodynamic functions Compared to the compounds studied this always indicates to higher kinetic stability and lower chemical reactivity.