Membrane trafficking between the plasma membrane (PM) and intracellular compartments is an important process that regulates the deposition and metabolism of cell wall polysaccharides. Dynamin-related proteins (DRPs), which function in membrane tubulation and vesiculation are closely associated with cell wall biogenesis. However, the molecular mechanisms by which DRPs participate in cell wall formation are poorly understood. Here, we report the functional characterization of Brittle Culm3 (BC3), a gene encoding OsDRP2B. Consistent with BC3's expression in mechanical tissues, the bc3 mutation reduces mechanical strength, which results from decreased cellulose content and altered secondary wall structure. OsDRP2B, one of three members of the DRP2 subfamily in rice, was identified as an authentic membrane-associated dynamin via in vitro biochemical analyses. Subcellular localization of fluorescence-tagged OsDRP2B and several compartment markers in protoplast cells showed that this protein not only lies at the PM and the clathrin-mediated vesicles but also is targeted to the trans-Golgi network (TGN). An FM4-64 uptake assay in transgenic plants that express green fluorescent protein-tagged OsDRP2B verified its involvement in an endocytic pathway. BC3 mutation and overexpression altered the abundance of cellulose synthase catalytic subunit 4 (OsCESA4) in the PM and in the endomembrane systems. All of these findings lead us to conclude that OsDRP2B participates in the endocytic pathway probably as well as in post-Golgi membrane trafficking. Mutation of OsDRP2B disturbs the membrane trafficking that is essential for normal cellulose biosynthesis of the secondary cell wall, thereby leading to inferior mechanical properties in rice plants.