Abstract: Disclosed is a modular roof skylight system which includes channel shaped roof and ceiling panel assemblies locked together with a skylight panel assembly therebetween. The skylight panel assembly includes roof and ceiling light transmitting sections which may be installed in place of and between modular roof panels. The inner ceiling skylight panel is securely mounted to the adjacent ceiling panels by a pair of flexible mounting clips complementally formed relative to elongated ceiling support strips secured to the adjacent ceiling panels. The support strips are formed with a plurality of serrations along one inner face. Each mounting clip is likewise formed with a plurality of mating ridges. A first of the mounting strips is secured on one side of the skylight panel opening with the serrations exposed for mating with a mounting clip. A second of the mounting strips is secured on an opposite side of the skylight opening with the serrations secured against the adjacent ceiling panel.