The Wally’s Festival of Fun will take place at Kirkstall Abbey between 11am and 4pm on Sunday, June 10.
John Puddephatt, of co-organisers Kirkstall Valley Development Trust, said: “We’ll be attempting to set a world record for the largest gathering of Wallys in a single place, with 4,626 the number we need to beat.
“To help us in our bid, would-be Wallys need to wear a red and white striped hat and T-shirt, blue jeans and specs in order to be counted.”
The count will take place at 2pm, and aims to beat the current record set by the people of Nagasaki in Japan last year.
A Wally dog competition will also take place.
The free event will put on a range of other activities, such as improvised comedy and games, aimed at people of all ages while raising money for mental health charities in the city.