American companies based in the region remain generally optimistic about business prospects for the 10 markets of Asean.
The findings came in the annual Asean Business Outlook Survey by the United States Chamber of Commerce and the American Chamber of Commerce Singapore (AmCham).
A total of 471 senior executives, representing US companies in all 10 Asean countries, took part in the survey in May and June.
Nearly three-quarters - 72 per cent - of senior executives polled in the survey reported that their company's level of trade and investment in Asean has risen over the past two years, and 86 per cent of them expect it to increase over the next five years.
US Chamber of Commerce's senior vice-president of Asia, Ms Tami Overby, said: "This survey demonstrates that US business remains confident about prospects in Asean. However, this confidence cannot be taken for granted."
Despite upbeat sentiment from most respondents, the study also found that there has been a shift in terms of how these business leaders see Asean's role in contributing to their worldwide revenues now.
More than half - 53 per cent - of respondents said that Asean markets have become more important in terms of their companies' worldwide revenue over the past two years. However, this is 10 percentage points lower than that reported in 2013.
Also, two-thirds, or 66 per cent, of respondents this year expect Asean to become more important in terms of worldwide revenues over the next two years. But the figure is down seven percentage points from two years earlier.
Of respondents said their company's level of trade and investment in Asean has risen during the past two years
Expect it to increase over the next five years
In the survey, US companies identified various concerns and impediments to their growth in the region.
Corruption was cited as the top issue and most respondents in all countries, except Singapore, believe that a lack of efficient enforcement of the law will hinder their future operations.
These companies also highlighted burdensome laws and regulations, lack of transparency, poor quality of infrastructure, and the difficulty in moving products through customs in some countries as obstacles to greater investment.
According to the survey, Singapore continues to be attractive to companies because of its strengths - good infrastructure and personal security, a stable government and political system, as well as a lack of corruption.
However, companies based here face challenges over the availability of low-cost labour and housing and office-lease costs.