According to the Daily Express, Suu Kyi had appealed against her conviction in August for breaking terms of her last period of house arrest.
But government sources said the Rangoon division court had ruled against the appeal.
Already in detention for about 14 of the last 20 years, Suu Kyi was sentenced to another 18 months of house arrest for sheltering an uninvited American at her home for two days in May.
In the appeal, Suu Kyi's lawyers raised no new substantive arguments that had not been heard in the original district court trial.
Burma's courts almost always follow the same hard line towards Suu Kyi and the country's democracy movement, which the military government often accuses of collaborating with the country's enemies to destroy the nation.