"We commend Taiwan for being one of the freest societies in the world," Pelosi told Taiwan's parliament.
She also said new US legislation aimed at strengthening the American chip industry to compete with China "offers greater opportunity for US-Taiwan economic cooperation."
While Pelosi is not the first House Speaker to go to Taiwan - Newt Gingrich visited in 1997 - her visit comes as relations between Beijing and Washington have deteriorated sharply, and with China a much more powerful economic, military and geopolitical force than it was a quarter century ago.
China considers Taiwan part of its territory and has never renounced using force to bring it under its control. The United States warned China against using the visit as a pretext for military action against Taiwan.
Early on Wednesday, China's customs department announced a suspension of imports of citrus fruits, chilled white striped hairtail and frozen horse mackerel from Taiwan, while its commerce ministry suspended export of natural sand to Taiwan.
A long-time China critic, especially on human rights, Pelosi was set to meet later on Wednesday with a former Tiananman activist, a Hong Kong bookseller who had been detained by China and a Taiwanese activist recently released by China, people familiar with the matter said.