A POLYPHENOL INCREASING AGENT FOR PLANT LEAVES, A POLYPHENOL AND AMINO ACID INCREASING AGENT FOR PLANT LEAVES, A RESIN PELLET, A PLANT LEAF STORAGE SHEET, AND A METHOD FOR MANUFACTURING A PLANT LEAF STORAGE SHEET WHICH CAN IMPROVE THE STORABILITY OF THE PLANT LEAVES SUCH AS LEAFY VEGETABLES AND TEA LEAVES ARE PROVIDED. A POLYPHENOL INCREASING AGENT FOR PLANT LEAVES COMPRISES PROANTHOCYANIDINS AND TREHALOSE. THE POLYPHENOL INCREASING AGENT FOR PLANT LEAVES PREFERABLY COMPRISES PROANTHOCYANIDINS AND TREHALOSE AT A WEIGHT RATIO OF 1:15 TO 1:60. A PLANT LEAF STORAGE SHEET COMPRISES THE POLYPHENOL INCREASING AGENT FOR PLANT LEAVES.