In applying to engineering structural materials, the mechanical properties of mica flake reinforced plastics, which now used extensively as dielectric and insulation materials, were experimented. Mica flake was classified in three groups according to their average aspect ratio and pregnated in epoxy and unsaturated polyester resin. Mica flake reinforced composites were molded by compression molding technique, then, flexural modulus and tensile strength of the composites were tested with respect to the aspect ratio and volume fraction of flake. Compared with experimental results and theories we obtained; The practical factor, K, that reflect the departure from theoritical behavior can be evaluated as K_e=0.4~0.5 (in flexural modulus) K_t=0.6~0.8 (in tensile strength). The major factor which reduce the mechanical strength in flake reinforced composites by compresstion technique is considered as flake-flake lapping and reduction rate of aspect ratio, L_p caused from the lapping is L_p=1/4-1/2