The influence of tacticity on the mechanical properties of polypropylene-Low density polyethylene (PP-LDPE) blends is investigated by tensile measurements in Instron machine. The testing was performed at constant cross head speed. Research grade isotactic PP, atactic PP and a commercial PP are separately blended with the same LDPE at all composition ratios. Haake melt blender was used at 50 rpm and 10 min of blending. Adequate amounts of antioxidants were added to preserve samples from degradation during melt blending. The influence of cross head speed and composition on small and large strain properties was assessed. Thermal analysis is used to support to evaluate crystallinity and correlate results to modulus. The results of mechanical testing were used to infer structure-property relationships for PP/LDPE blends.