The speed, angular, and alignment distributions of S(D-1(2)) atoms from the ultraviolet photodissociation of OCS have been measured by a photofragment imaging technique. From the excitation wavelength dependence of the scattering distribution of S(D-1(2)), the excited slates accessed by photoabsorption were assigned to the A＇ Renner-Teller component of the (1)Delta and the A"((1)Sigma(-)) states. It was found that the dissociation from the A＇ state gives rise to high- and low-speed fragments, while the A" slate only provides the high-speed fragment. In order to elucidate the dissociation dynamics, in particular the bimodal speed distribution of S atoms, two-dimensional potential energy surfaces of OCS were calculated fur the C-S stretch and bending coordinates by nb initio molecular orbital (MO) configuration interaction (CI) method. Conical intersections of (1)Delta and (1)Sigma(-) with (1)Pi were found as adiabatic dissociation pathways. Wave packet calculations on these adiabatic surfaces, however, did not reproduce the low-speed component of S(D-1(2)) fragments. The discrepancy regarding the slow S atoms was attributed to the dissociation induced by nonadiabatic transition from A＇((1)Delta) to A＇((1)Sigma(+)) in the bending coordinate. This hypothesis was confirmed by wave packet calculations including nonadiabatic transitions. The slow recoil speed of S atoms in the nonadiabatic dissociation channel is due to more efficient conversion of bending energy into CO rotation than the adiabatic dissociation on the upper slate surface. By analyzing the experimental data, taking into account the alignment of S(D-1(2)) atoms, we determined the yield of the nonadiabatic transition from the A＇((1)Delta) to the ground states to be 0.31 in the dissociation at 223 nm. Our theoretical model has predicted a prominent structure in the absorption spectrum due to a Feshbach resonance in dissociation, while an action spectrum of jet-cooled OCS measured by monitoring S(D-1(2)) exhibited only broad structure, indicating the limitation of our model calculations.