The innovative 3D weaving method allows I-beams to be woven in one piece and promises to eliminate delamination failure with the interlacing yarns. Therefore, woven I-beam composites have been developed to improve the resistance of laminated I-beam composite structures against delamination. In this study, woven I-beam fabrics (IBFs) were produced by the 3D weaving method by using 300, 600, and 1200 TEX E-glass fibers with a custom-built weaving machine. Then, IBFs were made into woven I-beam composites (IBCs) using the vacuum infusion method (VIP) to examine the influence of linear density on the mechanical properties of IBCs. The results of the three-point bending test represent that 300 TEX, 600 TEX (warp density: 20 ends/cm), 600 TEX (warp density: 12 ends/cm), and 1200 TEX samples had an average maximum flexural stress of 8.6, 9.2, 8.5, and 8.8 MPa, respectively. The compression strengths for 300 TEX, 600 TEX (warp density: 20 ends/cm), 600 TEX (warp density: 12 ends/cm), and 1200 TEX were 2.6 MPa, 3.8 MPa, 2.9 MPa, and 4.1 MPa, respectively.