Cartesian three-dimensional braiding as a method of preforming for hybrid composites has been investigated. The fundamental case of a two-sided hybrid 3-D braid was chosen. Hybrid preforms, along with a corresponding set of non-hybrid preforms for control, were fabricated using a Cartesian braiding method. The preforms were consolidated through a Resin Transfer Molding process and prepared for characterization and mechanical testing. Characterization of the braided hybrid composite specimens included yarn packing and deformation within an assumed unit cell, and measurement of constituent tow fiber volume fraction using digital image analysis. A comparison study of the elastic performance of Kevlar/epoxy and carbon/Kevlar hybrid composites was carried out. The tension test results show a near-linear stress-strain relationship for both specimen types within the range of the applied load. The tensile modulus for the carbon/epoxy and hybrid composite were found to be 41 GPa and 74 GPa, respectively. In addition, the Poisson ratio of near unity for both specimen types strongly suggests a fiber dominated material response. The difference in hybrid composite transverse strain due to the differing constituent fiberous materials is found to be appreciable. It is believed that this discrepancy in Poisson contraction, between the carbon and Kevlar sides of the specimens, causes the propagation of transverse cracks [primarily within the carbon tows] and ultimately leads to catastrophic composite failure. Composite ultimate strength and strain to failure were found to be 793 MPa and 1.9% for the Kevlar/epoxy sample and 896 MPa and 1.1% for the carbon/Kevlar hybrid.