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Liquid-state ionic thermocells (LITCs) can effectively convert low-grade waste heat to electricity. However, the larger structural dimensions and lower power density of LITCs restrict their large-scale practical application in scenarios with limited operating space such as photovoltaics, automotive applications, data centers, etc. In the present work, we demonstrate a micro-ionic thermocell (MiTC) with micrometer-scale structural dimensions prepared by soft lithography, which can synergistically promote the entropy change of the solvation structure and mass transfer of redox ions, and thus ionic thermoelectric properties. The effects of electrolyte concentration, scale effect and interface charge of the microstructure, and electrode gap on the ionic thermopower and Pmax/ΔT2 of MiTCs were comprehensively investigated to reveal the enhancement mechanisms using UV-vis/FTIR/in situ Raman analyses. The interfacial effect of microstructure-electrolyte solution can boost ionic reactions and transport processes at the microscale. It can increase the ionic thermopower and conductivity of 0.4 mol L−1 Fe(CN)64−/Fe(CN)63− electrolytes in MiTCs from −1.4 mV K−1 and 147.6 mS cm−1 to −2.5 mV K−1 and 254.2 mS cm−1, thus reaching a high Pmax/ΔT2 value of 15.4 mW m−2 K−2 at a 2 mm electrode gap and 50 μm microstructure width, respectively, showing a significant enhancement. Combined with microfabrication technology, MiTCs can facilely achieve large-scale integrated stacking and output considerable electricity within limited structural dimensions to meet the practical requirements for the integration and miniaturization of low-grade heat harvesting. [ABSTRACT FROM AUTHOR]