During the week-long trip starting Tuesday, Nationalist Party Chairman Lien Chan will meet with Chinese President Hu Jintao.
President Chen had threatened to charge Mr. Lien with treason if he signs any deals without government permission. But on Sunday, Mr. Chen softened his stance, saying Mr. Lien could use the trip to explore the possibility of reconciliation.
China passed legislation last month to legalize military action if Taiwan declares independence.
The upcoming trip will be the first time a leader of the Nationalists has visited the mainland since the Communists won a civil war in 1949 and the Nationalists fled to Taiwan.
Some information for this report provided by AP, AFP, Reuters.