Photoinduced volume expansion and contraction in hydrogenated amorphous silicon (a-Si:H) films have been studied, Photoinduced volume contraction seems to occur in a-Si:H films having hydrogen contents less than similar to5 at.%. The wavelength dependence of the photoinduced volume expansion indicates that one of driving forces of this phenomenon may be relaxation energy of photoexcited carriers. The reciprocity relation between light intensity and illumination time does not hold both in photoinduced volume expansion and photodegradation. The mechanism of the photoinduced volume changes is also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.