In this Letter, we focus on investigating the ultrafast photonics applications of two -layer HfS3 nanosheets. We prepared two -layer HfS3 nanosheets and carried out experiments to study their nonlinear saturable absorption properties. The results showed that the two -layer HfS3-based saturable absorber exhibited a modulation depth of 16.8%. Additionally, we conducted theoretical calculations using first principles to estimate the structural and electronic band properties of the two -layer HfS3 material. Furthermore, we utilized the two -layer HfS3 materials as SAs in an erbiumdoped fiber cavity to generate mode -locked laser pulses. We measured a repetition frequency of 8.74 MHz, a pulse duration of 540 fs, and a signal-to-noise ratio of 77 dB. Overall, our findings demonstrate that the two -layer HfS3 material can serve as a reliable saturable absorber, possessing properties comparable to currently used two-dimensional materials. This expands the application fields of HfS3 materials and highlights their potential for advanced optoelectronic devices. (c) 2024 Optica Publishing Group