The bell towers are located on both sides of the front of the church and originally had flat roofs. It was not until 1895 that the church added two pyramidal roofs to cover the belfry according to the design of the architect Gardes. Because these roofs were built with zinc materials, they are also called the "zinc towers".

The zinc towers help give the building its own unique mark to be different from Notre Dame Cathedral in Paris (France) and these zinc towers are clear expressions of the Gothic architectural style at Notre Dame Cathedral. In addition, because the Notre Dame Cathedral has a prominent height, the zinc towers are the place to install lightning rods to protect the building from lightning damage..

The bell tower has a total of six bells with six sounds, hanging on two bell towers. This set of bells were made in France and brought to Saigon in 1879.

Looking from the outside, on the right tower there are 4 bells (Sol, Do, Re, Mi); the left tower hangs 2 bells (La, Si). The surface of each bell is decorated with very elaborate motifs. The total weight of the bell set is about 27 tons. If we take into account the counterweight system (1,840 kg) attached to each bell, the total weight of the bell set will be nearly 29 tons.

The bells are all controlled by electricity from below. Three of the large bells are started by pedaling (because they are too heavy) before switching on the power switch. On weekdays, the church only rings one Mi bell at 5 am and the Re bell at 4:15 pm. On holidays and Sundays, the church usually rings three bells according to the chords Mi, Re and Do (actually the chord of three bells Mi, Do and Sol, but because the Sol bell is too heavy, it is replaced by the Re bell). Only on Christmas Eve are all six bells rung. The bell tolls as far as 10km as the crow flies.