• It is the first time to achieved a harmonic mode-locking fiber laser based on TaSe 2 . • 128th harmonic mode-locked pulses at 908.8 MHz repetition rate are stably generated. • The work provides a new solution for generating high repetition frequency pulses. Passively harmonic mode locking of an erbium-doped fiber laser based on TaSe 2 nanosheets saturable absorber (SA) is demonstrated. The TaSe 2 nanosheets are prepared by the liquid phase exfoliation technology and then deposited onto side surface of a D-shaped fiber to form a fiber-compatible TaSe 2 SA. The balanced twin-detector method is utilized to measure nonlinear absorption characterization of the fabricated SA, which gives saturable absorption, nonsaturable absorption, and saturation intensity as 5.49%, 24.6%, and 89.2 MW/cm 2 , respectively. Then, TaSe 2 SA is inserted into a passively mode-locked erbium-doped fiber laser, and the fiber laser is demonstrated with a fundamental frequency of 7.1 MHz. By adjusting the polarization controller and pump power, harmonic mode-locking operation is realized. As the pump power increases to 380 mw, 128th harmonic mode-locked pulses at 908.8 MHz repetition rate are stably generated. The results confirm that TaSe 2 is indeed a very desirable photonic material, which can be used in photonics, fiber optic communication, laser material processing and light modulators.