Ga1−xMnxAs nanowires were synthesized with finely controlled Mn contents (x = 0, 0.01, 0.02, 0.03, and 0.05) by the vapor transport method. They consisted of single-crystalline GaAs nanocrystals (avg. diameter = 60 nm) grown along the [111] direction. The Mn doping decreases the lattice constant, most significantly at x ≈ 0.03. X-ray photoelectron spectroscopy revealed that as the Mn content increases, the binding energy of Ga 2p shifts to a higher energy, which can be correlated with the hybridization between the Mn2+ ions and the holes. X-ray absorption spectroscopy and X-ray magnetic circular dichroism confirmed that the Mn2+ ions substitute into the tetrahedrally coordinated Ga sites and that the magnetic moment is maximized at x = 0.03, where the lattice constant is minimized and the binding energy of Ga 2p is maximized. The magnetization measurement revealed that all of these nanowires exhibited room-temperature ferromagnetic behavior, which is also observed most significantly for x ≈ 0.03.