The council had said it could not stop people smoking in Ynysangharad Park
"No Smoking" signs will be installed at a children's play area after a father complained about adults smoking.
When Nicholas Powell took his three-year-old daughter to Ynysangharad Park in Pontypridd town centre, he found adults smoking on benches.
"It's not very nice for children breathing in the smoke and watching adults smoking," said Mr Powell.
Rhondda Cynon Taf council said it would extend the signs to other play areas if the scheme was a success.
Dave Batten, head of leisure, parks and countryside at Rhondda Cynon Taf council, said: "We are in the process of preparing notices to be displayed around the children's play area in Ynysangharad War Memorial Park.
"These notices will request that park users refrain from smoking in that area."
Mr Powell, a school business manager and community councillor from Beddau, first wrote to the council a year ago asking for the smoking ban to be extended to the play area.
But he was told the ban only covered enclosed places.
However, this year he wrote again when he noticed "No Smoking" signs had been placed at a paddling pool and outside the cafe.
Mr Batten said smoking was not illegal in these areas and the signs were in fact "polite notices".
But he agreed to put up notices in the play area and to extend the signs around the council area if the scheme was successful.
Mr Powell said he was not against smoking in general but was worried children would want to copy adults when they saw them with cigarettes.
"I'm not saying you shouldn't smoke within the park itself.
"But people wouldn't think about doing it in a school," he said.