Wa Lone and Kyaw Soe Oo were arrested while carrying official documents which had just been given to them by police officers.
They have maintained their innocence, saying they were set up by police. The case has been widely seen as a test of press freedom in Myanmar.
"I have no fear," Wa Lone, one of the two journalists, said after the verdict. "I have not done anything wrong. I believe in justice, democracy and freedom."
The two men, who both have families with young children, have been in prison since their arrest in December 2017.
"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.
Judge Ye Lwin told the court in Yangon the pair had "intended to harm the interests of the state". "And so they have been found guilty under the state secrets act," he said.
Wa Lone, 32, and Kyaw Soe Oo, 28, had been collecting evidence about the execution of 10 men by the army in the village of Inn Din in northern Rakhine.
During their investigation, they were offered documents by two police officers, but were arrested immediately afterwards for the possession of those documents.
Authorities later launched their own probe into the killings, confirming the massacre took place and promising to take action against those who had taken part.
BBC Myanmar correspondent Nick Beake in Yangon said many would see this verdict as a crushing blow to freedom of the press in Myanmar and another setback for democracy, three years after Aung San Suu Kyi's party triumphed in free elections.
He said Wa Lone and Kyaw Soe Oo bowed their heads as the verdict was delivered. The reporters have always insisted they were framed. Wa Lone - who has missed the birth of his first child while being detained - protested his innocence once again as he was led away.
