Abstract: Multi-walled carbon nanotubes water-surfactant suspensions were prepared by ultrasonication, and the optical limiting curves were measured for 1 064 nm, 10 ns Nd:YAG Q-switched puled laser. The experimental results indicated that the output energy varied linearly with input fluences at a lower level, when the incident fluences increase to about 160 mJ/cm2, the output was clamped and tended to the value 16 mJ finally, and the transmittance of the sample decreased from 71% to 15%. In addition, the optical limiting mechanisms were investigated through performing Z-scan, pump-probe and 45° scattering experiments. The results show that the nonlinear scattering dominates the transmittance losses and the nonlinear refraction is secondary.