The electronic structure, intramolecular interactions, second-order delocalizations, and C-N rotational barriers in aminoguanidine have been studied using ab initio MO and density functional methods. Isomer AGI with intramolecular hydrogen bonding has been found to be the most stable on the potential energy surface, with nine minima. The influences of the basis set, computational method, and solvent effect on relative stabilities of important isomers of aminoguanidine have been studied. Natural Population Analysis (NPA) indicates that amino substitution in guanidine leads to an increased electron delocalization from the center of the NH2 attachment to the 7 frame. A strong redistribution of 7 electron density has been observed in aminoguanidine in relation to guanidine. The protonation energy for aminoguanidine is slightly less than that of guanidine. In protonated aminoguanidine, the pi delocalization is more polarized in comparison to that in protonated guanidine. NPA, HOMA, and NICS studies have been carried out to understand electron delocalization in protonated guanidine and aminoguanidine.