A dual-wavelength synchronously mode-locked homogeneously broadened bulk laser operating at 1985.6 and 1989 nm is presented for the first time, to the best of our knowledge, which delivers a maximum output power of 166 mW and a repetition rate of 85 MHz. The pulse duration was measured to be 16.8 ps by assuming a ${\mathrm{s}\mathrm{ech}}^2$ pulse shape. The recorded autocorrelation trace showed frequency beating signals with an interval of 3.8 ps and a full width at half-maximum duration of 2 ps, corresponding to an ultrahigh beating frequency of about 0.26 THz, which agrees well with the frequency difference of the emitted two spectral peaks. The results indicated that such a kind of dual-wavelength mode-locked Tm:YAlO₃ laser could be potentially used for generating terahertz radiations.