The rate coefficients for the reactions of hydrogen (H) atom with propylene and isobutylene were studied at M06-2X/6-31+G(d,p) and MPWB1K/6-31+G(d,p) level of theories between 200 and 2500 K. The possible mechanism for the reactions of propylene and isobutylene with H atom were examined. The rate coefficients for each reaction channels were calculated over a wide range of temperature using Conventional Transition State Theory (CTST). The quantum mechanical tunneling effect was computed using parabolic model and were included in the rate coefficient calculations. The Arrhenius expressions for the reactions, propylene + H and isobutylene + H were estimated to be k_{propylene+H} = (9.68 ± 0.17) × 10^{−18} T^{2.16}exp[−(131 ± 10)/T] cm^{3} molecule^{−1} s^{−1} and k_{isobutylene+H} = (1.40 ± 0.22) × 10^{−16} T^{1.89}exp[−(215 ± 12)/T] cm^{3} molecule^{−1} s^{−1}, respectively. Theoretically calculated rate coefficients are found to be in good agreement with the available experimentally measured rate coefficients.