The aim of this study was to study the mechanical properties of woven bamboo fiber (WBF) reinforced polypropylene (PP) composites. The bamboo fiber mat was constructed manually by hand. The WBF/PP composites were fabricated by thermoforming process. The basic characteristics of the bamboo strips, such as density, cross section, and tensile properties were measured first. The strengths of the bamboo strip in different sizes were measured, and they were around 400 MPa after 5 wt% alkali treatment. The WBF/PP composite with alkali treated bamboo fibers had better tensile strength than that with untreated bamboo fibers. The strength and modulus are about two times larger in longitudinal direction, while they are about the same in the transverse direction. For the hygrothermal aging test, the composites were highly sensitive to moisture, which could degrade the composites mechanical properties. In the bamboo fiber preforming process, the moisture can enhance the formability of the woven bamboo fiber mat and prevent the bamboo fiber to spring back after forming. The experimental results implied that the preforming of the woven bamboo fiber mat into complex shape is feasible under the wet condition.