A polypropylene was filled with 0 to 30 wt.-% of flaky fillers such as glass flake, mica, or talc, which had similar particle sizes and different aspect ratios and crystallization temperatures. Flexural test specimens were injection-molded from the filled polypropylenes at cylinder temperatures of 200 to 320-degrees-C Properties such as flexural modulus, flexural strength, heat distortion temperature, Izod impact strength, and mold shrinkage and higher-order structures such as crystallinity, beta-crystal content, thickness of skin layer, a*-axis-oriented component fraction, and crystalline orientation fraction were measured and structure-property relationships were studied. A simulation of molecular orientation was carried out from a viewpoint of melt orientation at the gate and its relaxation in the mold cavity.