Resource-rich but poor Myanmar has a history of engagement with Beijing, but Washington has recently sought closer ties with the quasi-civilian government, easing some sanctions to reward the end of military rule.
Speaking at the World Economic Forum on East Asia in Bangkok, in her first trip abroad for 24 years, Suu Kyi said she was worried about the two superpowers jostling for position over her country.
"A lot of people are talking now about what the position of Burma will be now that we are starting to engage... more with the United States and how it will affect our relations with China," she told reporters, using Myanmar's former name.
"I'm always very concerned when Burma is seen as a battling ground for the United States and China.
"It should not be so, it should be an area of harmony for those two big countries," she said, adding that Myanmar and China had been "good neighbours" for many years.
Critics accuse China of extracting natural resources at the expense of Myanmar's impoverished people, and helping to shield the country's former junta from the full weight of international opprobrium at the UN Security Council.
In a rare sop to public opinion, Myanmar last year halted construction of a $3.6 billion Chinese-backed dam project, risking the ire of Beijing, its second-largest trading partner and biggest foreign investor.
The US has sought to build links with President Thein Sein's government, easing some investment sanctions and naming its first ambassador to the country in 22 years, to reward steps towards democracy including by-elections in April.
But Washington has vowed to keep broad sanctions against Myanmar as an "insurance policy" against "backsliding" on democratic reforms even as it seeks to open up certain types of investment.
Myanmar occupies a key strategic position between neighbours China and India and its gas, oil, water, wood and precious stones are widely coveted by foreign investors.
Indian Prime Minister Manmohan Singh visited Myanmar this week, signing trade deals and meeting Suu Kyi, as part of efforts to boost links and contest the influence of regional rival China.