Catalytic growth of high-purity GaN nanowires is achieved at temperatures of 750 and 620 degreesC using gallium acetylacetonate and ammonia gas. The straight single-crystal GaN nanowires with diameters in the range 15-60 nm are found to grow following the vermicular-like nanowires on Si(100) substrate at 750 degreesC via a vapor-liquid-solid (VLS) mechanism using Ni as a catalyst. Photoluminescence (PL) characteristics of the GaN nanowires show a UV emission peak ranging from 360 to 420 nm at room temperature. Successful growth of GaN nanowires at low temperatures is suggested to be due to sufficient gallium precursor provided by gallium acetylacetonate during synthesis.