The ambipolar diffusion coefficient of (110) GaAs/AlGaAs multiple quantum wells was measured by the transient spin grating technique.The ambipolar diffusion coefficient and carrier life time,which are Da=13.0 cm2/s and τR=1.9 ns,were obtained directly by this technique under carrier concentration nex=3.4×1010/cm2 at room temperature.The measured Da keeps almost a constant value when the photoexcited carrier concentration is increased up to 1.2×1011/cm2.