This study investigated Young’s moduli of polypropylene (PP) composites containing acicular wollastonite crystal (AWC). Three different loadings of AWC (10 wt%, 20 wt%, and 30 wt%) were incorporated into the PP composites. The morphology of the AWC within polypropylene was examined using a scanning electron microscope. Tensile tests demonstrated that when the loading of the AWC increased, the moduli of the polypropylene composites increased accordingly. Subsequently, the moduli of the composites were characterized using multiscale simulation incorporating the aspect ratio of AWC. In multiscale simulation, the orthotropic properties of AWC were evaluated through molecular dynamics simulation. Subsequently, the mechanical properties of PP composites were predicted based on the Mori–Tanaka micromechanical model together with the properties of the ingredient materials. The results indicated that the moduli of the composites derived from the multiscale simulation are in close agreement with the experimental data.