A Metal-Semiconductor-Metal (MSM) ultraviolet photodetector was fabricated on the un-doped n-Al0.3Ga0.7N grown by Metal-Organic Chemical Vapor Deposition (MOCVD). The detector exhibited a sharp cutoff at the wavelength of 300nm, which was in accordance with the band gap of Al0.3Ga0.7N. It had dark currents of 1pA and 1nA at the biases of 2.5V and 6.5V respectively and had a responsivity of 0.038A/W at the bias of 1V and at the wavelength of 298nm.