The survey, which was carried out between February and June, assessed the Bengal tiger population across a 600-mile stretch in Nepal and India. It found numbers had increased in all of Nepal's national parks.
South Asian governments have committed to doubling tiger populations by 2022, but the animals continue to face threats from poaching and habitat loss. There are thought to be fewer than 2,000 tigers left worldwide, with 60% of them in India.
The survey covered tigers in the Terai Arc region, which spreads across the north Indian states of Bihar, Uttar Pradesh and Uttarakhand and into southern Nepal.
Nepal's survey concentrated on five protected areas and three wildlife corridors.
The results show the number of tigers in Nepal have increased to 198, a rise from 121 in 2009. In particular, the tiger population in the south-western Bardia national park has risen from about 18 in 2009 to 50 this year.
Nepalese officials described the findings as a "milestone" in the bid to double the number of wild tigers by 2022, as agreed by the region's leaders at an international summit in 2010.
"Tigers are a part of Nepal's natural wealth and we are committed to ensuring these magnificent wild cats have the prey, protection and space to thrive," the director-general of Nepal's Department of National Parks and Wildlife Conservation, Megh Bahadur Pandey, said.
Tens of thousands of Royal Bengal tigers, the most numerous subspecies of tiger, used to roam Bangladesh, Bhutan, India and Nepal, but their numbers have fallen dramatically in recent decades.