[Problem] To provide a polyphenol increasing agent for plant leaves that enables an increase in the storage life of plant leaves such as leaf vegetables and tea 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. [Solution] A polyphenol increasing agent for plant leaves contains proanthocyanidin and trehalose. The polyphenol increasing agent for plant leaves preferably contains proanthocyanidin and trehalose at a weight ratio within 1 : 15 to 1 : 60. A plant leaf storage sheet contains the polyphenol increasing agent for plant leaves.