In this paper, in order to investigate the basic mechanical property and the variation of mechanical property of T800 carbon/epoxy composites according to the forming pressures, the various tensile tests were carried out for the in-plane mechanical properties such as E1, E2, G12 and Poisson ratios according to the international testing standards (ASTM 3039 for the unidirectional properties and ASTM 3518 for the bias extension test for in-plane shear properties).