Based on positron annihilation experiments combined with first-principles calculations, magic vacancy clusters in two typical covalent materials, graphite (sp(2)) and Si (sp(3)), are reported. In the experiments, ample vacancies in graphite and Si samples were introduced by neutron irradiation. The samples were isochronally annealed to high temperature, and then positron lifetime and angular correlation of annihilation radiation (ACAR) were measured. For graphite, it is observed that the longer positron lifetime is stable to higher-dose irradiation and for high-temperature (up to 1500 degreesC) post-irradiation annealing. Especially, both the lifetime and 2D-ACAR distribution are found to agree well with the calculated ones for the V-6 of six-membered ring using a first-principles pseudopotential plane-wave method. These findings clearly evidence the magic V6 ring in graphite. For Si, the longer lifetimes corresponding to the magic V-6 (puckered) ring and V-10 cage (consisting of four V-6 rings) were observed after annealing above 500 degreesC, demonstrating vividly the coexisting and evolution of the magic vacancy clusters in Si.