Wa Lone and Kyaw Soe Oo were arrested last year while carrying official documents which had just been given to them by police.
The case has been widely seen as a test of press freedom in Myanmar.
They have maintained their innocence, saying they were set up by police.
"Today is a sad day for Myanmar, Reuters journalists Wa Lone and Kyaw Soe Oo, and press freedom anywhere," said Reuters editor-in-chief Stephen Adler.
The verdict comes a year after the crisis in Rakhine state came to a head when a Rohingya militant group attacked several police posts.
The military responded with a brutal crackdown against the Rohingya minority. The UN has said leading army figures in Myanmar should be investigated and prosecuted for genocide.
Media access to Rakhine is strictly controlled by the government so it is difficult to get reliable news from the region.