Double cantilever beam (DCB) and instrumented microtome cutting (IMC) tests were carried out in testing wood fracture properties of control and various transgenic poplar plants. The results show that control plants have higher work of fracture (WF) than most transgenic plants. The air-dry materials have higher WF than wet ones and latewood is higher than earlywood. Also, samples from parts of the trunk above stye points usually have higher WF than those from below. The comparison between DCB tests and IMC studies show that, the WF obtained from DCB is higher than the cutting work measured by IMC. Scanning electronic microscopy (SEM) and confocal laser scanning microscopy (CLSM) were used to study specimensfracture surfaces and structure. Though in all samples fracture occurred between the middle lamella and S1layers, between S1 and S2 layers, as well as within S2 layers, there are more transwall fractures in control plants.There are also differences in cell wall area fraction among these materials.