Manganese oxide nanosheets (MnO2 NSs) with two-dimensional formation and typically ultrathin thickness have gained a great deal of attention due to their excellent physical and chemical properties. However, the potential capability of MnO2 NSs in laser application has been rarely explored. Here, we first report the MnO2 NSs as the saturable absorber (SA) for generating Q-switched pulsed laser. The MnO2 NSs-based SA not only shows a broadband absorption, but also possesses nonlinear saturable absorption feature. By integrating the MnO2 NSs-SA into an erbium-doped fiber laser cavity, a stable passively Q-switched operation at central wavelength of ∼1558 nm was realized with a threshold pump power of 220 mW, and 1.26 µs pulse width with a repetition rate of 92.35 kHz was obtained. Our results indicate that the MnO2 NSs can serve as promising candidates for constructing optical pulsed lasers.