This method for fabricating alloy for solar cell involves mixing copper, indium, gallium, selenium and sulfur raw materials, vacuum-sealing the same in an ampoule, heating the ampoule, and crystallizing the raw materials within the ampoule by melt-growth. The copper, indium and gallium raw materials are transformed into copper indium gallium (CIG) crystals, and these CIG crystals may be crushed or powdered. By doing so, it is possible to obtain high-quality crystals in crystallization with S or Se. The cooper indium gallium crystals are prepared in two steps: a vacuum-sealing step in which copper, indium and gallium raw materials are mixed and vacuum-sealed in an ampoule; and a CIG crystallization step in which the ampoule is heated, and the raw materials within the ampoule are crystallized by melt-growth. CIG crystals can be crushed, and if mixed with selenium alone, can be transformed into a quaternary alloy.