A detailed fracture mechanics analysis of bridge-toughening in a fiberreinforced composite is presented in this paper.The integral equation governing bridge-toughening as well as crack opening displacement (COD) for the composite withinterfacial layer is derived from the Castigliano’s theorem and interface shear-lagmodel.A numerical result of the COD equation is obtained using the iteration solutionof the second Fredholm integral equation.In order to investigate the effect of variousparameters on the toughening,an approximate analytical solution of the equation ispresent and its error analysis is performed,which demonstrates the approximatesolution to be appropriate.A parametric study of the influence of the crack length,interracial shear modules,thickness of the interphase,fiber radius,fiber volumefraction and properties of materials on composite toughening is therefore carried out.The results are useful for experimental demonstration and toughening design includingthe fabrication process of the composite. A detailed fracture mechanics analysis of bridge-toughening in a fiberreinforced composite is presented in this paper. The integral equation governing bridge-toughening as well as crack opening displacement (COD) for the composite withinterfacial layer is derived from the Castigliano’s theorem and interface shear- lagmodel. A numerical result of the COD equation is obtained using the iteration solution of the second Fredholm integral equation. In order to investigate the effect of variousparameters on the toughening, an approximate analytical solution of the equation ispresent and its error analysis is performed, which demonstrates the approximatesolution to be appropriate. A parametric study of the influence of the crack length, interracial shear modules, thickness of the interphase, fiber radius, fiber volume fraction and properties of materials on composite toughening is therefore carried out. The results are useful for experimental demonstration and toughening design including the fabrication pro cess of the composite.