The probability characteristics of the concentration fluctuation in pollutant plume dispersion in a neutral stratified atmospheric boundary layer were investigated experimentally in a wind tunnel experiment. It was examined using a tracer gas without buoyancy, which emitted from a fixed point in the ground surface. The diffusion fields in the boundary layer were examined using an isolated building model. Instantaneous concentration fluctuations were measured along the mean plume centerline at various downwind distances from the source at different heights with the frequency of 1KHz. Probabililistic analysis was performed on the concentration fluctuation, and results were presented for probability density functions (PDF) of mean concentration, fluctuation intensity and crosswind mean-plume dispersion. Furthermore, the effects of turbulence intensity on the statistical nature of concentration fluctuations were presented and discussed. Probability density functions of the concentration fluctuation data have shown a significant nonGaussian behavior. The lognormal distribution appeared to be the best fit to the shape of actual probability density functions of fluctuating concentration measured in the boundary layer wind flows in a wind tunnel. The plume dispersion PDF near the source was observed shorter than that those far from the source.