The optical absorption spectra were investigated to study the electronic structures of perovskite-type proton conductors. The fundamental absorption edge shifts to higher energy side when an acceptor ion was doped to the perovskite-type oxides. In SrZrO3, an absorption band was observed in the lower energy side of the fundamental absorption edge when an acceptor was doped. It is suggested that this band corresponds to the acceptor level of the proton conductors. The absorption of this band was enhanced when the proton was removed from the crystal. This suggests that the number of electrons in the acceptor level decreases when a proton is introduced to the crystal.