We demonstrate a C-band wavelength-tunable microlaser with an Er3+-doped high quality (∼1.8×106) lithium niobate microdisk resonator. With a 976 nm continuous-wave pump laser, lasing action can be observed at a pump power threshold lower than 400 µW at room temperature. Furthermore, the microdisk laser wavelength can be tuned by varying the pump laser power, showing a tuning efficiency of ∼-17.03pm/mW at low pump power below 13 mW, and 10.58 pm/mW at high pump power above 13 mW.