This study aimed at investigating factors affecting the stability as well as structural properties of different indole isomers based on Density Functional Theory (DFT) calculations at B3LYP/6-311+G** theoretical level. Important thermochemical parameters (enthalpy, entropy and free energy of Gibbs) were employed to determine the stability on this isomer series. Qualitative relationships between relative stabilities for indole, isoindole and indolizine were obtained. In addition, the length of bond's average was used as parameter to corroborate thermochemical data. Finally, HOMO-LUMO gaps (ΔE), electro-negativity (μ), hardness (η), softness (ζ), electrophilicity (ω) and structural parameters were also calculated in the same theoretical level. The results show that indolizine is the most stable than isoindole and indole systems, respectively.