The movement of nanoparticles in fluids is one of the main factors that result in the remarkable thermal conductivity of nanofluids. In this paper, Laser speckle velocimetry (LSV) is proposed to measure the velocities of nanoparticles in nanofluids, and traditional LSV system is modified in order to be competent for detecting the movements of nanoparticles. It is verified that speckles can indeed be formed by illuminating laser beam on nanofluids by the means of experiments and numerical simulations. According to the modified experimental setup, a physical model is established. Based on statistical properties of speckles, the relationship between the movements of nanoparticles and the movements of speckles on the screen is studied by formula deduction. A conclusion is drawn that the velocities of nanoparticles is identical to the velocities of speckles in Fresnel region. Thereafter, the experimental system is set up, and speckle patterns sequences are recorded with high speed CCD camera. Two consecutive speckle patterns are processed with computer programs to obtain the motion vector diagram of speckles, thereby the motion of nanoparticles.