"The message that I bring from the US government is one of reaffirming the deep partnership the United States has with Taiwan in terms of security, commerce, health care and shared common values of democracy, economic freedom and liberty," he told reporters before his meeting with Tsai.
Azar has previously been critical of Beijing's response to the coronavirus, which began in central China, as well as the WHO.
It was a theme he repeated on Monday.
"[Taiwan] knew very early on... to not trust some of the assertions coming out of there [Beijing] or validation from the World Health Organization," he said.
As well as meeting Tsai, Azar will hold talks with his counterpart Chen Shih-chung and Foreign Minister Joseph Wu.
Testing China
Taiwan has become a poster child for defeating the coronavirus thanks to a well-honed track and tracing program as well as firm border controls.
Despite its proximity and economic links to China, it has recorded fewer than 500 infections and seven deaths.
In contrast, the US has recorded the most deaths in the world with more than 160,000 fatalities.
Critics have accused US President Donald Trump of ramping up criticism of China as a way to divert from growing public anger over his administration's coronavirus response, especially as he fights for re-election in November.