The launch took place at 3:37 p.m. local time (07:37 GMT) from the Wenchang Space Launch Site on Hainan using the Long March 5 carrier rocket.
The module separated from the carrier rocket and entered the target orbit about 8 minutes after the launch.
Mengtian will be the second and final laboratory module on the Chinese orbital station, and the equipment it carries will be used to study microgravity and conduct experiments in fluid physics, materials science, combustion science and basic physics.
The construction of the multi-module Tiangong space station officially began in April 2021, when the Tianhe core module was successfully launched into orbit. The main module is equipped with two docking ports for experimental compartments, as well as three docking ports for manned and cargo ships.
Another lab module, Wentian, successfully docked to the Chinese space station in July.
Tiangong will be considered fully complete when the Mengtian lab cabin module attaches to it, after which the station will become T-shaped and weigh about 66 tonnes. The station can host up to six people at the same time during a crew rotation change. The operational life of the station is 15 years and should end in 2038.