Microstructural design is a promising strategy to enhance the toughness and plasticity of structural ceramics while maintaining their inherently excellent hardness, which can facilitate their applications in extreme environments. In this work, the possibility of establishing a symbiotic structure with metal atomic-layer phase-separation (MALPS) in carbide structural ceramics was investigated. The carbide ceramic samples were synthesized from raw materials comprising transition metals with different component numbers, graphite powders, and a small amount of aluminum by spark plasma sintering at 1900 ℃ and under a pressure of 30 MPa. It was found that Al-MALPS structure was observed exclusively in the high-entropy (TiZrHfNbTa)C ceramic, which was not a MAX phase with long-range-order but rather a composite featuring a non-periodic cross-stacking of single metal atomic layers within the carbide matrix. Characterization by spherical aberration correction transmission electron microscopy and energy dispersive spectroscopy from nanometer to atomic scales revealed that the single Al atomic layers were sparsely embedded onto the {111} planes of the carbide face-centered cubic structure. Combined with the first-principles calculations, the formation of MALPS structure was found to be driven by thermodynamic stability, lattice distortion, and sluggish-diffusion effect of high entropy, rather than the differential diffusion of Al in various carbide lattices. This work could promote the design and regulation of atomic-scale microstructures in structural ceramics, aiming for high performance with synergetic high hardness-strength-toughness.