Peripheral plasma electrostatic fluctuations are studied with an inserted electrostatic probe array in the STP-3(M) Reversed Field Pinch, and radial profiles of electron density, electron temperature, and plasma space potential are measured. The particle flux driven by electrostatic fluctuation is calculated with the correlation between the fluctuation of electron density and fluctuation of plasma space potential, yielding the result that the increase of electrostatic fluctuation at the edge causes particle diffusions. The agreement between the E-r x B drift velocity of the radial electric field by the gradient of plasma space potential and the ion thermal velocity at the edge indicates ion motion dominates the particle diffusion. The decrease of the toroidal phase velocity at the edge and the confinement degradation shows the radial outside flow of the E-t x B-p drift, where E-t is generated by the toroidal flow fluctuationof the E-r X B drift. Therefore, the electrostatic fluctuation caused by the radial propagation of plasma space potential is thought of as the dominance of the radial particle flux. (C) 2004 Wiley Periodicals, Inc.