The effects of light intensity and external sucrose on the vase life of cut roses were estimated by monitoring the net photosynthesis and chlorophyll fluorescence. Cut flowers were held under different light intensities 10 (L10) or 50 (L50) μmol‧m-2‧s-1 with or without treatment with external sucrose. We found substantial differences in stomatal conductance, photosynthesis rate, photosystem II (PSII) quantum efficiencies, specific fluxes, and vase life of the cut flowers when exposed to different light intensities. Light intensity at 50 μmol‧m-2‧s-1 increased photosynthesis capacity, thus delaying petal senescence and extending the vase life of cut flowers. L50 flowers maintained a high photosynthetic rate by reducing heat dissipation (DI0/RC) and increasing electron transport (ET0/TR0 and ET0/ABS) in the electron transport chain of the photosynthesis apparatus. The application of external sucrose extended the vase life of cut flowers by improving water balance and sustaining turgor pressure in the petals of the cut flowers. The net rate of photosynthesis of the cut flowers was increased by higher light intensity; however, it was not affected by the application of external sucrose. Our results indicate that the application of external sucrose is necessary to improve the longevity of cut flowers when endogenous sucrose production by photosynthesis is insufficient under low light conditions during the postharvest period. In addition, our results revealed that most of the photosynthetic parameters were significantly correlated with the vase life of cut rose flowers. Moreover, the relation between the rate of photosynthesis and chlorophyll fluorescence parameters indicates that the rise from the basic dark-adapted fluorescence yield to the maximum (OJIP transient) method can be used as a tool for the evaluation and prediction of the photosynthesis rate in cut flowers.