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Polypropylene (PP) has been widely researched in power cable insulation due to its excellent resistance against high temperatures and high voltages. Since PP is too stiff for power cable extrusion, elastomers have been blended with PP to improve its stiffness. Although effects of elastomers on electro‐mechanical properties of PP have been widely studied, fundamental issues governing changes in dielectric properties of PP/elastomer blends have yet to be fully understood. This paper therefore reports on the properties of PP blended with ethylene‐based elastomer (EBE) and propylene‐based elastomer (PBE) by correlating their structural, mechanical, and dielectric investigations with respect to elastomer types and contents. The results show that blending increasing amounts of EBE and PBE improves mechanical flexibility of PP, with Young's modulus reduces by 53% at 40 wt% of elastomer content. Morphology‐wise, PBE demonstrates better compatibility with PP and less disrupted crystallinity compared to EBE. Furthermore, PP/PBE has better breakdown performance over PP/EBE, albeit that their breakdown strengths reduce with increasing elastomer contents. Specifically, direct current breakdown strength of PP/PBE reduces by only 21% at 40 wt% of PBE loading compared to 31% at equivalent EBE loading. Potential mechanisms governing breakdown changes are discussed with structural, mechanical, and dielectric interpretations. [ABSTRACT FROM AUTHOR]