In this report, we examined the influence of reflective film mulching (RFM) on the photosynthetic activity of carnation. In the RFM plot 32% of downward light was reflected while in the black mulching plot, 3%, and the photosynthetic rate increased by 32% on a seedling basis compared with the black mulching plot. However, the photosynthetic rate on a single leaf basis increased by only 16% at most by supplemental illumination. Higher ¹⁴CO₂ fixation in lower leaves was observed in the RFM plot, and a larger amount of assimilation products translocated to roots and folded leaves than in the black mulching plot. It is assumed that the higher photosynthetic activity in the case of RFM was caused by the activation of CO₂ fixation of lower leaves rather than by the increase of CO₂ fixation of each leaf in an individual plant.