Two novel poly(ester-urethanes) (PEUs: PEUa and PEUb) were reinforced by blending in a batch mixer with organic and inorganic fillers of different particle sizes and shapes. In most experiments the filler contents were 0, 5, 15, 30, and 50 wt.%. In general, both the particulate and fibre-like fillers increased the stiffness almost linearly with increasing filler content, but the tensile and impact strengths and strain at break showed a downward trend. Exceptionally, improvements in tensile strength were achieved with glass fibre, as expected, and, surprisingly, also with some blend compositions containing silicate-type fillers. In addition, slightly improved impact strength was achieved with a small amount of fine talc. Dynamic-mechanical thermal analysis confirmed the reinforcing effects and showed some slight changes in the glass transition temperature of the PEU. Scanning electron microscopy studies on the morphology revealed relatively good mixing and contact between all the fillers and PEU.