She said she wants to see for herself whether new civilian leaders are ready to throw off 50 years of military dictatorship. Clinton will also encourage leaders to sever military and nuclear ties with North Korea.
The U.S. and other Western nations suspect Myanmar has sought and received nuclear advice along with ballistic missile technology from North Korea in violation of U.N. sanctions.
"I am obviously looking to determine for myself and on behalf of our government what is the intention of the current government with respect to continuing reforms both political and economic," Clinton said before her arrival.
This is the first time a U.S. secretary of state has visited Myanmar in more than half a century.
Clinton will meet senior Myanmar officials including President Thein Sein in the capital Naypyidaw on Thursday before heading to the commercial capital of Yangon. There she will see opposition leader and Nobel peace laureate Aung San Suu Kyi, who is returning to the political scene after decades of detention and harassment.
Clinton declined to discuss specific steps that she would suggest to the military-backed government or say how the U.S. might reciprocate for positive change.
U.S. officials are cautious about what Clinton's three-day visit can accomplish beyond being a symbolic stamp of approval for the small steps of political and social reform under way since elections last year. There are no immediate plans to lift heavy U.S. sanctions on Myanmar imposed because of an abysmal human rights record.
The Associated Press contributed to this report.