The purpose of this study is to investigate the mechanical and thermal properties of polypropylene reinforced with colemanite particles. Tensile, impact, hardness, Differential Scanning Calorimetry and Termomechanical Analysis tests were used. Also, MFR was done for manufacturing datas. According to results obtained from Melt Flow Rate (MFR) test, infilling with colemanite 5% by volume (12.99% by weight) provides approximately 70 degrees C production temperature saving. It was detected that ground colemanite substance increased the elastic modulus and especially greatly increased the breaking strain while it decreased the yield stress and the yield strain of the material. But it is nearly the same for breaking stress. It can be observed that the addition of colemanite to polymer matrix make a decrease in its thermal expansion coefficient. This reduction can be attributed to lower thermal expansion coefficient of colemanite, respect to polymer matrix.