"We also congratulate" Myanmar, she told reporters on the sidelines of a summit of the Association of Southeast Asian Nations (ASEAN) in Cambodia.
"The election has been very clear and peaceful so I think that is good for ASEAN."
She said Thailand supported democratic reform in Myanmar, where the military has eased its grip on power over the past two years and allowed the opposition to participate in politics.
Nobel peace laureate Suu Kyi, a former political prisoner, will enter parliament for the first time after winning a seat in Sunday's by-elections.
Her National League for Democracy party secured 40 of the 44 seats it contested, according to partial official results.