We investigated thermal leptogenesis scenarios in the left-right symmetric extension of the standard model. In the SO(10) GUT framework, we impose the D-parity realization below GUT scale. These two conditions makes our model more restrictive and predictive. In such a case, a D-parity odd singlet in the 4-index antisymmetric tensor representation of SO(10) have a critical role. This singlet have prospects of causing a very large mass hierarchy between SU(2)L and SU(2)R triplet scalars. We test our model by computing baryogenesis via leptogenesis. The heavy right-handed neutrinos N's and the SU(2)L triplet scalar can generate the lepton number asymmetry. Leptogenesis scenarios can be categorized by these mass scales. If the light neutrinos are Majorana and have a hierarchical mass spectrum, we can obtain a successful result in leptogenesis through lightest N-decay. But we found that the normal mass hierarchy of the light neutrinos conflicts with leptogenesis through triplet-decay.