Composites are advanced engineering materials which have succeeded in replacing many metal structures in the industry due to their unique properties such as high strength, good resistance to corrosion and abrasion, light weight and good fatigue strength. Sandwich composites are one of the composite structures which have attracted the attention of many experts due to good mechanical performance. One of the main problems for applying the conventional sandwich composites is the structural delamination when they exposed to different loading. In order to avoid this problem, in this research, 3D spacer structures produced by knitting techniques have been used as composite reinforcement. The results of previous researches show that these structures do not present good mechanical performance in bending loading due to the low stiffness of the knitted fabrics. To improve the flexural performance of these structures, the surface layers of the spacer structures can be reinforced with straight yarns in weft and warp directions. So far, there is no report on the flexural performance of these composite structures in the literatures. Therefore, in this research, the effect of warp and weft yarns associated in the Multi-Cellular spacer weft-knitted fabrics, on the bending properties of the resulted composites is investigated. All Multi-Cellular spacer weft-knitted fabrics with rectangular cross-sectional core were produced in one and double decker shape on a modern flat knitting machine using glass fibers. Continuing this process, glass wrap and weft yarns were inserted in the outer layers of spacer structures. Fabric characteristics such as loop length and stitch density were the same for all samples. Then, three-dimensional composites were manufactured using RTM method. In order to investigate the mechanical behaviour of glass/epoxy composites, the samples were subjected to three-point bending loading. Statistical analysis confirms that the structure cross-section and the reinforcing yarns have significant effect on the composite flexural strength. The results revealed that the maximum bending force of single and double decker structures reinforced with warp and weft yarns increases 75% and 62.5% compared with non-reinforced composites, respectively. Finally, to predict the mechanical behaviour of the produced 3D composites, the structure was modeled in the Abacus software using macro-scaled finite element method. The results showed good compatibility between experimental and simulation results.