Polyimide (Pl) composites dispersed with poly(p-phenylene terephthalamide) (PPTA) gel were prepared and the mechanical properties of the composites were investigated. The modulus of composite, where the PPTA as a liquid crystalline polymer was finely dispersed in the PI matrix, was increased remarkably even with the incorporation of PPTA of about 1 wt%. In order to interpret these phenomena, a lattlce model was applied and the relationships between structures and properties were analyzed by optical microscopy, scanning electron microscopy (SEM), tensile tester. The fine dispersions of PPTA in PI matrix phase were observed in the micrographs of SEM. The polarized optical microscopic images observed from stepwise imidization showed the crystallinity of PPTA dispersed in PI matrix to become higher during the imidization. It was concluded that PI/PPTA composites prepared in this work almost approach the molecular composite system which has a extreme reinforcement potential, and that the estimated modulus of a PPTA single itself in the matrix is considered to approach the theoretical modulus of a PPTA single crystallite.