Interfiber bonding is a critical parameter for the strength properties of cellulosic material. In this study, confocal laser scanning microscopy (CLSM) was applied to determine the interfiber bonded area of lignocellulosic fibers. Based on its unique features of optical sectioning, a series of 2D images were obtained. The optically bonded area, which does not include the unbonded area, and the overlapped area were estimated. The bonding ratio of the interfiber network, defined as the optically bonded area to the total overlapped area, was also estimated. Furthermore, the 3D-image reconstructions of the interfiber bonded model were established. The developed CLSM technique was applied to a poplar high-yield pulp sample.