1/f noise characteristics of hydrogenated HgCdTe photodiode have been investigated. The hydrogenated diodes have better 1/f noise characteristics than typical ion implanted or plasma-induced junction diodes. In order to investigate the origin of the noise reduction, infrared transmission of the HgCdTe was measured. The absorption edge shift and infrared transmission enhancement were observed in hydrogenated samples, which means that the hydrogenation can passivate point defects or residual impurities in HgCdTe. The carrier mobility increment and concentration reduction were also observed in hydrogenated HgCdTe.