We investigate and discuss spin polarization effects on cyclohexane (C₆H₁₂) dehydrogenation with a Ni atom, by performing total energy calculations based on the density functional theory (DFT). We consider the process where cyclohexane approaches the Ni atom, and determine the reaction paths from the calculated potential energy surfaces (PESs) for singlet and triplet systems. The C-H bond dissociation processes of the cyclohexane for both singlet and triplet systems are almost the same. After interacting with the Ni atom, the Ni atom draws an H atom from the cyclohexane, and an H-Ni bond is formed. With the C-H bond broken, cyclohexyl intermediate (C₆H₁₁) separates from the Ni atom. For the triplet system, however, no energy is required to separate the cyclohexyl from the H-Ni system due to the repulsion between up-spin electrons, resulting from the up-spin electron transfer from the Ni atom to the C atom. Therefore, it indicates that the magnetic properties of the Ni atom are favorable for the cyclohexane dehydrogenation. [DOI: 10.1380/ejssnt.2004.200]