Taiwan's President Ma Ying-jeou is due to leave for the Vatican on Sunday to attend the inauguration mass of Pope Francis in a move that has stoked tensions with China.
The Vatican is one of the 23 states that recognise Taipei as independent of Beijing and is Taiwan's only diplomatic ally in Europe.
China still refuses to renounce the possible use of force against the island in its long-stated goal of re-taking Taiwan, which has ruled itself since the end of a civil war in 1949.
Although cross-strait ties have warmed up in recent years, China bitterly opposes any steps that imply recognition of Taiwan by other countries, including their hosting visits by senior government leaders from the island.
The Vatican has said it would welcome Ma joining other foreign dignitaries who will attend the installation of Pope Francis on Tuesday, adding that it would "receive him with every honour".
"I really look forward to this visit ... I'd like to extend Taiwanese people's sincere gratitude and well-wishes to the Vatican," Ma wrote in a message posted on his Facebook page prior to his departure.
He is due to board a flight to Rome late Sunday night.
China's foreign ministry spokeswoman Hua Chunying called on Taiwan to "bear in mind the overall situation and deal prudently with sensitive issues" at a regular press briefing on Friday.
"We hope that the Vatican will take concrete steps to create conditions for the improvement of China-Vatican relations and gradually remove barriers," she added.
Hua has also called on the Vatican to sever its diplomatic ties with Taiwan and to "recognise the Chinese government as the sole legal representative of all China".
China's communist regime broke ties with the Vatican in 1951 and six years later set up its own Catholic church, which does not recognise the pope as its head.
The last time Taiwan's leader visited the Vatican was in 2005, when then president Chen Shui-bian attended the funeral of Pope John Paul II.
An incensed Beijing refused to send a representative and filed a protest to Italy for issuing Chen a visa.