In this project, I investigate the photoconductivenature of photochromic rare-earth metal oxy hydrides (REMHO). Such materials have received increasingscientific attention since they show a color-neutralphotochromic effect that can be applied, e.g., in smartwindows or chromogenic devices. Photochromicmaterials reversibly turn opaque from transparentunder illumination with light of optical wavelength. Inrecent studies it was found that these materials alsoshow an instant decrease in resistivity whenilluminated which can be used in optical sensors. Tounderstand the nature of this photoconductive effect,I grew yttrium oxy hydride thin films by reactivemagnetron sputtering. I measured the resistivity forillumination from front and substrate side, opticaltransmission and compositions of the samples andrelated the results to photoconductivity. I show thatphotoconductivity is a bulk effect and not directlyrelated to photochromism. Samples that almost lostphotochromism due to aging, still show strongphotoconductivity. Moreover, it was observed that theresistance increased faster during bleaching for frontillumination than for back illumination.