People making the trip for the 2019 Rugby World Cup in Japan should consider getting vaccinated against it, if they plan on visiting rural parts of the country, it said.
Over 600,000 international fans are expected to visit Japan, and with just over a month to go until the tournament kicks off, campaigners are trying to raise awareness of the disease which is spread through mosquito bites.
Japanese encephalitis affects approximately 68,000 people worldwide each year, with between 13,600 to 20,400 of reported cases being fatal, according to the World Health Organization.
The Encephalitis Society believe travelling fans should take the necessary precautions before making the trip to East Asia.
Dr. Ava Easton, chief executive of the charity, told Sky News: "The message for the Rugby World Cup is that travel health is important, and this campaign that we are running, is encouraging fans travelling to Japan to seek specialist travel health advice which is appropriate to their plans and destinations.
"If they're just flying in, just to watch the matches in the cities, then really, they probably don't need any kind of vaccines. But people don't just do that, they often extend their stays and see much of what's a very beautiful country.
"And if they're going to be spending extended periods in the countryside, then vaccination is maybe something that they want to talk to a specialist travel health adviser about before they go."
The former England rugby player John Bentley, a supporter of the campaign, has mirrored Easton's message, saying: "Supporters, not just rugby players, won't just take in the rugby, they will take in all different aspects of the country and embrace the culture, and perhaps travel into areas where they could be vulnerable."
The tournament kicks off on September 20, when Japan takes on Russia in the opening match.
England and the USA face each other in their opening games on September 26.