We report on the demonstration of a passively Q-switched 1.55 µm fiber laser utilizing a colloidal PbS quantum dot (QD) thin film as a saturable absorber. Colloidal PbS QD films have several features that are advantageous in passively Q-switched fiber laser operation, including a large operation wavelength range, cost-effectiveness, and a low saturable absorption intensity. We conducted thorough material and optical studies to verify the advantages of PbS QDs in Q-switched laser operation and successfully generated 801 nJ pulses with a 24.2 kHz repetition rate. To the best of our knowledge, the developed Q-switched fiber laser is the first based on colloidal PbS QDs.