Abstract: Quartz fiber reinforced composites are often used in multi-field coupling environments. To ensure enough interlaminar performances, quartz fiber reinforced composites often exist in the form of 2.5D braided structures. In this paper, the three dimensional mechanical properties of a 2.5D quartz fiber reinforced bismaleimide resin composites (shallow bend-joint) were comprehensively tested. The tensile and compressive properties in different directions, and in-plane and out-of-plane shear property were compared and analyzed. It has been found that the tensile and compressive module of the warp direction are slightly higher than those of the weft direction, while the tensile and compressive strenghth of the warp direction are significantly higher than those of the weft direction. Tensile and compressive failure modes of the material in the warp and weft direction are significantly different. In case of tension, the waved warp fibers are pulled out, and the straight weft fibers are split. In case of compression, the straight weft fibers are broken, and the waved warp fibers buckling happen. The material shows high shear deformation capacities in both the in-plane and out-of-plane directions. Besides, a formula for estimating the tensile modulus of the 2.5D material was proposed based on the rule of mixtures of unidirectional composites. Based on the microstructure characteristics of the material, a unit cell containing warp and weft yarns was used as a representative volume unit to establish the finite element model, and the meridional modulus of the 2.5D woven composite was predicted. The prediction results are in good agreement with the experimental results. This study can provide some guidance for the development of the 2.5D quartz fiber/bismaleimide composites.