Lilac Lark is being held in Withdean Park from 12.30pm to 5pm.
Activities on offer include stalls, such as a coconut shy, tombola, crafts, bric-a-brac, plants and refreshments, as well as Punch and Judy and other live entertainment and a popular dog show.
Withdean Park is renowned for its lilac bushes and May is the best time to see them in bloom.
The park has the second largest collection of lilacs in the world with over 250 different types.
It was designated the National Lilac Collection by the National Council for the Conservation of Plants and Gardens in 1982 and Brighton Council was awarded the President’s Award by the International Lilac Society in 1986.
However, council cutbacks affected the upkeep of the collection and it lost its national status in 2009.
In the same year thieves armed with secateurs targeted the park and cut off many hundreds of branches and blooms shortly before the lilac festival, threatening the future of the plants.
But the bushes survived and the flowers remain an impressive seasonal sight.