We demonstrate for the first time to our knowledge the use of Fe3O4 nanoparticles for Q-switching a tunable mid-infrared (Mid-IR) Dy3+-doped ZBLAN fiber laser around 3 μm. The Q-switcher was fabricated by depositing the prepared Fe3O4 nanoparticles solution onto an Au mirror. Its nonlinear optical response was characterized using a mode locked Ho3+/Pr3+-codoped ZBLAN fiber laser at 2.87 μm, and showed a modulation depth of 11.9% as well as a saturation intensity of 1.44MW/cm2. Inserting the device into a tunable Dy3+-doped ZBLAN fiber laser, stable Q-switched pulses within the tunable range of 2812.4–3031.6 nm were obtained. When tuning the wavelength to 2931.2 nm, a maximum Q-switching output power of 111.0 mW was achieved with a repetition rate of 123.0 kHz and a pulse width of 1.25 μs. The corresponding pulse energy was 0.90 μJ. This demonstration suggests that Fe3O4 nanoparticles are a promising broadband saturable absorption material for mid-infrared operation.