Yttrium oxide (Y2O3) has garnered some attention in view of its potential to be integrated into a wide range of high-strength structural components, microelectronic and optoelectronic devices. However, the nonlinear optical research of this promising material has not been implemented yet. In this paper, not only the electronic band structures of Y2O3 are theoretically calculated but also the optical nonlinearity of Y2O3 is validated by using the fiber laser as a platform. Meanwhile, the influence of sample thickness on laser performance is further explored by using Y2O3 saturable absorbers with different thickness. Results indicate that Y2O3 not only has impressive optical nonlinearity but also is beneficial to the investigation of ultrafast photons by adjusting the thickness of Y2O3. Therefore, Y2O3 can be used as a potential saturable absorber candidate for in-depth research and application.