Geometrical structures and relative stability of gauche and trans butyronitrile conformers have been investigated by utilizing ab initioab initio and DFT calculations. The results showed that the gauche conformer is more stable by 0.27 kcal/mol, outlined as enthalpy change ΔH between the two conformers, at CCSD/6-311G+(d,p), the highest level of theory used. Also, the population analysis displays that the gauche conformer is present at 70% in the gas phase, more predominant than the trans conformer. These results agree well with the previousexperimental and theoretical findings. Additionally, thermodynamic properties of the two conformers have been investigated. The data exhibit that the abundance of the gauche conformer increases as the temperature decreases under high-pressure condition. The results help to understand the reasons behind the conformational transitions between the fluid and the solid phases.