This paper presents an experimental study on the fire behavior of glass fiber-reinforced polymer (GFRP) load- carrying slabs for building and bridge applications. Fire experiments were performed on cellular full-scale slabs with and without internal liquid cooling. The slabs were subjected to serviceability limit state loads during ISO 834 fire exposure from the underside. Liquid cooling was demonstrated to be an effective way of improving the fire endurance. The code-required 90-minute fire resistance for buildings was met. After an increase in the first 20 min, temperatures, deflections, and axial strains of the liquid- cooled slabs approached a nearly steady-state condition in the 70–100 min that followed. The remaining total safety factor in post-fire experiments was greater than 3.3 and therefore still sufficient to prevent structural collapse. The non-liquid cooled reference specimen provided structural resistance during fire exposure for 57 min. For bridge applications, it was concluded that the fire endurance of non-liquid cooled cellular GFRP bridge decks is sufficiently high in the case of fire from the underside.