The atmospheric oxidation mechanism of sabinene initiated by the OH radical has been studied using quantum chemistry calculations at the CBS-QB3 level and reaction kinetic calculations using transition state theory and unimolecular rate theory coupled with collisional energy transfer. The oxidation is initiated by OH radical additions to the CH 2 C< bond with a branching ratio of ∼(92−96)%, while all the hydrogen atom abstractions count for ∼(4−8)% of branching ratio, which was estimated by comparing the rate coefficients of the reactions of sabinene and sabinaketon with the OH radical. Addition of OH to the C< carbon forms radical adduct Ra, while addition of OH to the terminal CH 2 carbon forms radical adduct Rb, which would break the three-membered ring promptly and almost completely to radical Re. RRKM-ME calculations obtained fractional yields of 0.40, 0.09, and 0.51 for radicals syn-Ra, anti-Ra, and Re, respectively, at 298 K and 760 Torr. In the atmosphere, the syn/anti-Ra radical would ultimately transform to sabinaketone in the presence of ppbv levels of NO, while in the transformation of the Re radical, both bimolecular reactions and unimolecular H-migrations could occur competitively for the peroxy radicals formed. The H-migrations in peroxy radicals result in the formation of unsaturated multifunctional compounds containing >CO, −OH, and/or −OOH groups. Formation of sabinaketone from syn-and anti-Ra and formation of acetone from Re are predicted with yields of ∼0.37 and ∼0.38 in the presence of high NO, being larger than while in reasonable agreement with the experimental values of 0.19−0.23 and of 0.21−0.27, respectively.