Tens of thousands of protesters have taken part in a march and rally in Taipei highlighting the threats that Taiwan faces from mainland China.
"The great Taiwanese people oppose annexation and invasion," President Chen Shui-bian told the crowd.
Taiwan's future should be decided by its people, Mr Chen said.
Last year China passed a law to allow the use of force if Taiwan formally declares independence. China has more than 700 missiles targeted at Taiwan.
Police said about 45,000 people took part in the rally in front of the presidential office building.
The crowd carried banners that read "No Aggression, Protect Taiwan", or "We Want Democracy, We Want Human Rights".
"Our future will never be decided by the 1.3 billion people of China," Mr Chen told them.
"We are totally against unification. Our future will only be decided by the 23 million people of Taiwan."
Saturday's event also coincides with the 10th anniversary of China firing a series of missiles close to Taiwan which were seen as an attempt to influence the outcome of the island's first direct presidential elections.
Some legislators from the governing party have criticised the event as unnecessary and costly.
They argue that the party, which had a disastrous showing in last year's local elections, should try to win back public support by focusing on reform and improving the economy rather than taking to the streets, says the BBC's Caroline Gluck in Taipei.
The same message has come from the opposition parties, who held a large protest last week in which they called on the government to stop stoking tensions with China and concentrate on the economy, our correspondent says.