This paper provides the results of ten triaxial tests which were carried out to study the unsaturated shear strength characteristics of Shiraz silty clay soil. The soil tested was reconstituted using static compaction. Consolidated drained (CD) triaxial tests were performed on both saturated and unsaturated samples at various net confining pressures and matric suctions. Digital image processing technique is used to measure the total volume change of the specimens. The accuracy of this technique is discussed by comparing the results with the volume change of the saturated tests determined from the conventional method. The volume change is also used to determine the change in sample diameter which is used to correct the deviatoric stress accordingly. Shear strength parameters and are determined from the test results and dependence of parameter χ on soil suction is studied and compared with the available relationships in literature. Furthermore, it is shown that the shear strength of both saturated and unsaturated soil specimens fall on a single line in the effective stress space. Therefore, applicability of the effective stress principle for the shear strength of unsaturated Shiraz silty clay is clearly validated.