To obtain an agent for treating TGE and PED viral swine diarrhea, effective for treating the swine diarrhea caused by TGE virus and PED virus mainly proliferating in digestive tracks by compounding a polyphenol compound originating from tea.

This agent for preventing and treating swine viral diarrhea contains a polyphenol compound originating from tea. The agent is preferably added to a usual swine feed (including a substitute milk or an artificial milk), and the mixed feed is preferably fed to pigs. The agent is preferably added to the feed in an amount of 0.0005-2 wt.% as the polyphenol on the basis of the feed. It is preferable to continuously administer the agent to a pig over its all stages ranging from a lactated pig stage to an adult pig stage.