The unidirectional composite DCB specimen is considered as two finite length Timoshenko beams, attached together along a common edge except at the initial delamination length. Because of symmetry, only one half of the specimen is considered, which is partly free and partly resting on an elastic foundation. The problem is analytically solved by considering Timoshenko beam resting on Winkler and Pasternak elastic foundations and fracture toughness is generally derived. In the prior researches on this specimen using Timoshenko beam theory, the effect of the ligament length on the energy release rate was ignored. This research presents the solution for finite ligament length. Besides, the effect of ligament length on energy release rate and its minimum value that makes the energy release rate independent of the ligament length, is presented. For the special case when the ligament is large compared with the beam thickness, a closed form solution is derived for Timoshenko beam resting on Winkler elastic foundation. The analytical results are compared to prior researches on this subject and a good agreement is observed. The fracture toughness and compliance obtained by Timoshenko beam resting on Winkler elastic foundation predicts more accurate results with respect to experimental results.