Micro- and nanocubes of carbon have been synthesized by laser ablation in liquid. The morphology and structure analyses indicated that these micro- and nanocubes are single crystals with a body-centered cubic structure with a lattice constant of 5.46 angstroms, which is so-called C 8-like structure, and they have a slightly truncated shape bounded mainly by (200) facets. A blue-purple luminescence at room temperature was observed in the cathodoluminescence spectrum of the synthesized single micro- and nanocube of carbon, which exhibited that this unique carbon nanomaterial is a new semiconductor with blue luminescence. The physical and chemical mechanisms of the synthesis of carbon micro- and nanocubes were pursued upon laser ablation in liquid.