Wozniacki, yet to land a grand slam, started nervously as Peng landed the first set 6-2 but righted herself to win 2-6, 6-3, 6-3 and take her 16th career title.
The Dane had already gained a boost in the semis with her three-set win over reigning French Open champion Francesca Schiavone.
Wozniacki now heads for Paris where she faces Japan's Kimiko Date-Krumm in her first round match on the red clay.
Peng, ranked 31 in the world, had seen off number two seed Vera Zvonareva of Russia in her semi but was unable to capitalise on her strong start as Wozniacki roared back for her fourth title of the season having had treatment to her left thigh in the opening set.
"I needed this tournament to finalise my preparations for Roland Garros," said Wozniacki, who finally outlasted Peng after two hours and 35 minutes to add Brussels to title wins this campaign at Dubai, Indian Wells and Charleston.
- AFPTags: sport, tennis, belgium