The high-speed particle image velocimetry (PIV) is employed to measure the distribution of particle fluctuation velocity near the minimum conveying velocity in the acceleration and fully developed regimes in a horizontal pneumatic conveying. The fluctuation characteristics of particle velocity are examined in terms of time-averaged particle velocity and concentration, power spectrum, auto-correlation coefficients, two-point correlation coefficients, intensity of particle fluctuation velocity, skewness factor and probability density function. It is revealed that the profile of the time-averaged particle velocity depends on the conveying velocity and solids loading ratio in the bottom part of the pipe in the fully developed regime. A quasi-periodical particle flow pattern with the lower frequency appears in this region and dominates the pressure drop of the pneumatic conveying. The intensities of particle fluctuation velocity of the sliding strand flows in the bottom part of pipe are smaller that of the suspension flows in the top part of pipe, revealing that the low intensity of particle fluctuation velocity can result in the low conveying pressure drop. The particle fluctuation velocity of the low or minimum conveying velocity follows the Gaussian probability distribution in the fully developed regime. (C) 2011 Elsevier Ltd. All rights reserved.