It follows spectator feedback criticising the constant noise from fans who use horns to create regular or constant background noise during the on-the-field action.
Air horns are already banned from the stadium but the new rule now extends the ban to include all forms of horn such as the Vuvuzela and mouth activated devices.
Ground regulations for the Millennium Stadium have been updated to empower stewards to stop fans entering the venue with horns, confiscate the devices from those who use them or evict persistent offenders.
The new ruling will not cover the Speedway Grand Prix events at which the use of horns by fans is customary and commonplace.
Supporters who are aware of fans using horns at any other sporting event at the stadium will now be able to alert stewards and action will be taken.
Stewards will be briefed before each match to ensure the new rule is followed throughout all areas of the stadium.
The Millennium Stadium Manager, Mark Williams, said: “The ban on the use of all types of horn is now part of the terms and conditions for attendance at events.
“The Millennium Stadium enjoys a unique atmosphere which must be protected for the enjoyment of all 74,500 supporters who can attend games here.
“Our supporters are encouraged to generate noise through singing and shouting for their team but the intrusive use of these horns is extremely disruptive.
“We have received feedback from supporters who have said the constant sound from these horns has distracted their attention from the action on the field and ruined their enjoyment of the games.
“People come to the Stadium to have a good time and there is undoubtedly a party atmosphere at events, but we will not tolerate disruptive activities from individuals who do not show proper concern for their fellow fans.”
