Modal separation of work-of-fracture was carried out for unidirectional C/C composites in order to characterize their multi-modal fracture behavior. The C/C composites were prepared by filament winding method with a coal tar pitch as a matrix precursor, and followed by heat treatment at temperatures between 1000degreesC and 2800degreesC under argon flow. During single edge-notched beam tests, tensile fracture and interlaminar shear fracture were simultaneously observed in the specimens. In proportion to the fracture surface area, the total work done during fracture was divided into each fracture mode, and the modal work-of-fracture was obtained by dividing each modal dissipation energy by twice the corresponding modal fracture surface area. With increasing the heat treatment temperature, the modal work-of-fracture for the tensile mode gradually increased and reached a maximum of around 6 kJm(-2) at a heat treatment temperature of 2000degreesC, whereas the modal work-of-fracture for the interlaminar shear mode remained constant around 20 Jm(-2). Determination of these modal work-of-fracture values revealed quantitatively the contribution of each fracture mode to the total dissipation energy of the composites.