Abstract The potential role of metasomatism‐induced hydrated layers, such as amphibole, in causing the mid‐lithospheric discontinuities (MLDs) has been widely debated. To determine whether amphibole is the compositional cause of the MLDs, we measured the electrical conductivity of mixtures of olivine and various proportions of amphiboles under high pressures and temperatures. Our results showed that the amphibole reacted with the olivine at >1,023–1,173 K. Comparison of the geophysical observations with the electrical structure profiles calculated from this study constrained the amphibole contents of 20%–29% in MLDs in North China and South Australia, which may induce a 2.2%–3.1% reduction in seismic velocity.