Suu Kyi, detained for 15 of the past 21 years, was sentenced to a further 18 months of house arrest in August for allowing an uninvited American to stay in her lakeside home after he swam over to see her.
"The judge turned it down. He read out the decision but he didn't offer any reason for the rejection," her lawyer, Nyan Win, told reporters, who were barred from the courtroom.
Nyan Win said he planned to lodge an appeal against the decision with Myanmar's chief justice, the one remaining channel for Suu Kyi to seek her freedom.
"We will take it to an appellate court as soon as we know the details of the verdict," he added.
The verdict was widely expected by diplomats and activists, many of whom believe Myanmar's judicial system is beset by interference from the military, which has ruled the former Burma for almost half a century.
Home Minister Maj. Gen. Maung Oo said on Jan. 21 the 64-year-old Nobel Peace Prize winner would be released in November when her house arrest term expired, a comment Suu Kyi said was in contempt of court because her appeal had not been heard at that point..
Britain's ambassador to Myanmar, Andrew Heyn, said the coming election, the first in two decades, would not be credible unless Suu Kyi and other political prisoners were released.
"Although this decision came as no surprise, it's deeply disappointing," he told Reuters.
"If this year's elections are to have credibility and legitimacy, all shades of political opinion should have the opportunity to put their case to the electorate." The election, a date for which has yet to be revealed, has been widely derided as an attempt by the junta to make the country appear democratic, with the military pulling the strings behind a civilian-fronted government.
Suu Kyi's appeal centered on the legitimacy of the initial ruling, arguing that it should be overturned because the law she was charged under was obsolete, part of a 1974 constitution that was replaced in 2008 with a new charter.
She was found guilty of breaching a draconian security law protecting the state from "subversive elements" and initially sentenced to three years in prison, immediately commuted to 18 months of house arrest by the junta in recognition of her late father, independence hero Aung San.
Critics dismissed the case as a sham, a move by the junta to keep the charismatic and influential Nobel Peace Prize winner sidelined for the election. She was charged in May, just a few weeks before an earlier period of house arrest was due to end.
Aung Din, executive director of the Washington-based US Campaign for Burma, said the court's decision was expected because no judge would dare go against the will of the generals.
"The judiciary system in Burma is just a part of the regime's oppressive mechanism," he said in an e-mail.
"Anyone who challenges or threatens military rule will be hunted and arrested by police and intelligence (agents), imprisoned by judges, and kept in the dark by prison officials."
