Abstract: A transmission mechanism for a toner cartridge for use in a printing apparatus includes a transmission tenon provided with a plurality of radial ribs each having a first chamfer, and a transmission sleeve internally provided with a plurality of radial grooves. Each of the grooves includes a second chamfer at the opening end of the transmission sleeve. The number of the grooves is twice the number of the ribs, which provides more positions allowing the transmission tenon to engage with the transmission sleeve. Thus, the ribs can engage with the grooves more quickly and accurately, whereas the coupling of the chamfers can reduce contact interference and allows smoother movement transmission. The occurrence of malfunctions can be thereby reduced.