The incident had taken place in country's Dhading district, 75 kms west from here.
Ram Bahadur Damai and Kumbha Bahadur Sunar were handed down the sentence by Dhading district court around three years ago over the victim's complaint with the police.
The Supreme Court yesterday endorsed the verdict of the district court and upheld the judgement, rejecting the appeal of Kumbha for nullifying the charges.
The victim, in her complaint, had accused the duo of sexually assaulting her after consuming alcohol.