The preparation of ultrafine-grained dense ceramics at low temperatures is still a challenge, although several techniques for the same have been proposed. The primary limitation involves the simultaneous control of the nanoscale-grain size and elimination of the intergranular pores to maximize densification. Spark plasma sintering [7,8] and hot pressing [9,10], or hot isostatic pressing sintering [11], characterized by Surface activation and thermoplastic formation via an external field or force, can produce densified bulk materials rapidly at relatively low temperatures and with greatly suppressed grain growth, nevertheless expensive equipment and complicated operations restrict their further applications. Two-step sintering [12] also can achieve nearly full densification in nanocrystalline ceramics, such as Y2O3 [13], ZnO [14], BaTiO3 [15,16], and ZrO2 [17]. However, a temperature higher than that employed in the CSS method is often required to achieve the critical density, which then lays the foundation for the second step of sintering. Therefore, this approach is not very suitable for LTCC techniques, especially when electrodes with a low melting point are used. Cold sintering process (CSP) was recently proposed by Randal group [18], which provides a particular perspective for the preparation of nanocrystalline compacts at low temperatures. CSP involves the compaction of green pellets at a temperature 90% of the theoretical density), regardless of whether the materials are involved in congruent dissolution (Li2MoO4 [19], KH2PO4 [20], NaNO2 [20], ZnO [21], and ZrO2 [22], among others) or non-congruent dissolution (BaTiO3 [20] and Pb(Zr,Ti)O3 [23]), which is attributed to special liquid-phase creeping and dissolution–precipitation mechanisms. Further densification, and even full densification of the ceramics, could only be achieved by post-annealing at very a low temperature [18,23]. Therefore, the combination of nanopowder, CSP, and post-annealing is expected to easily prepare dense ceramics with the desired grain size with a low energy cost. The preparation of Li2Mg3TiO6 nanocrystalline ceramics proposed here outlines an approach that employs the CSP method.