Dynamic heterogeneity in PMMA/PVDF blends was systematically investigated with insights from microscopic dynamics to macroscopic properties. In this work, an initial attempt was made to understand the weak thermorheological complexity in the framework of chain entanglements. Intriguingly, the degree of thermorheological complexity displayed a composition dependence: PMMA-rich blends and PVDF-rich blends showed a slight thermorheological complexity, whereas blends with intermediate compositions exhibited a moderate one. Notably, inter-chain entanglement prevailed over the intra-chain entanglement in the former series of blends, whereas intra-chain entanglement dominated in the latter. The molecular entanglements were accordingly supposed to govern the scenario of thermorheological complexity. Local heterogeneity was observed to exist in the melt-state blends by in-situ dielectric relaxation spectroscopy (DRS); its molecular origin was depicted mainly due to the presence of interphase in the melt manifesting in the distinct Maxwell-Wagner-Sillars (MWS) relaxation. Further, the interphase in the melt was demonstrated to be evolved from the crystal-amorphous interphase in the solid crystalline blends and the corresponding molecular dynamics were evaluated by the electric modulus formalism. The relaxation dynamics in the interphase were found to be confined by the PMMA segments and vary as a function of composition: they were completely absent in PMMA-rich blends, but prominent in blends with intermediate compositions and reduced in PVDF-rich blends. This clearly indicates that interphase associated local heterogeneity in the melt also contribute to the overall dynamic heterogeneity. In addition, the glass transition temperature for blends appeared to satisfactorily follow the “self-concentration” model, suggesting the distinct distinct relaxation dynamics in components and therefore dynamic heterogeneity. Lastly, the effect of dynamic heterogeneity on the dynamic mechanical properties was further assessed.Zhang, Lamnawar et al.J. Rheol 2016; Lu Bo, Lamnawar, Maazouz, Soft Matter 2016.