This study clarified the role of the key enzymes [sucrose phosphate synthase (SPS), sucrose synthase (SS)] in the sucrose synthesis of eggplant (Solanum melongena L.) cultured on different polyethylene mulches. Sugar concentration in fruit and SPS and SS activities in leaf and fruit were measured during the different fruit development stages. Total sugar concentration was the highest on the reflective mulches throughout all the developmental stages of eggplant and followed by the white, the black, and transparent mulches. The concentrations of all three individual sugars (sucrose, glucose, and fructose) increased during fruit development on all four polyethylene mulches. Although no specific pattern in enzyme activities of leaf and fruit related to the sugar accumulation of eggplant fruit was observed, the reflective and white mulches triggered higher sucrose synthase enzyme activities than did the black and transparent mulches.