For many Sri Lankans, it is the first parliamentary election in which they can vote without fear of Tamil Tiger violence and suicide attacks after the rebels were defeated last year after three decades of conflict.
Rajapakse called the election two months ahead of schedule after his resounding victory in a presidential vote in January.
Opposition parties have accused Rajapakse's United People's Freedom Alliance (UPFA) of violating campaign norms and warned that Thursday's vote would not be free and fair, with his main political rival also behind bars.
But the charges are unlikely to have any major impact on voter intentions, which show a clear preference for the ruling party as it basks in the glow of Rajapakse's victory over the Tigers last May.
The crushing of the Liberation Tigers of Tamil Eelam (LTTE), which had been fighting for an ethnic Tamil homeland since 1972, was a major factor behind Rajapakse's re-election in January.
"We defeated the conspiracy to divide the country