The eatery owned by Ta Thi Thu Hien sits on Vo Chi Cong Street in Tay Ho District, near Nhat Tan Bridge.
All 29 seats were removed, and diners can easily see the vendor prepare bowls of pho through the open window.
Hien said her family bought the used coach from their friend for VND100 million ($4,000).
They then transformed it into a chicken noodle soup stall.
A bowl of pho here costs from VND60,000.
Diners can order side dishes like bagel twists, poached eggs and boneless chicken legs for VND5,000-30,000.
The restaurant has four waiters. Every day, the eatery consumes more than 30 kilograms of noodles and sells more than 150 bowls of pho within two to three hours.
The most crowded time is in the morning when diners typically enjoy their bowl of pho in a wide-open yard.