The trial run will last until the end of this month, according to the provincial portal.
The journey winds its way through popular tourist attractions in the city, such as the French-built Da Lat railway station, Hang Nga Crazy House, Rooster Church and other French heritage sites.
During the trial, three 37-seat buses will be pressed into service.
Situated on a plateau in the Central Highlands at around 1,500 meters above sea level, Da Lat enjoys year-round cool weather and is famous for its French colonial heritage.
Open-top tour buses are popular in many major cities around the world, including New York and Singapore.
The open-top bus service made its first appearance in Hanoi in 2017 before being launched in other tourist hotspots such as HCMC, Ha Long and Nha Trang.