We have experimentally demonstrated a dual-wavelength synchronously mode-locked Nd:CNGG laser based on the semiconductor saturable absorber mirror technique. Mode locking was achieved simultaneously on two gain bands of the crystal that have a central wavelength separation of $2.4\mathrm{nm}$ . The fundamental mode-locked pulse train has a repetition rate of $88\mathrm{MHz}$ and pulse duration of $5\mathrm{ps}$ , with an average output power of $\sim 90\mathrm{mW}$ . Autocorrelation measurements show that each of the synchronously mode-locked pulses consists of a train of quasi-periodic beat pulses with a $660\mathrm{fs}$ pulse width and a $0.63\mathrm{THz}$ repetition rate.