Abstract: The field experiment of ozone dry deposition over grassland was performed by using the concentration gradient method in the suburban area of Beijing which is often situated downwind of urban plumes and then influenced by high ozone concentration episode. The vertical profiles of ozone concentration and meteorological parameters were measured in early autumn (23 September－13 October 2007) in a valley of Mangshan Forest Park. Strict data quality control procedures were performed to guarantee the credibility of following analysis. Results show that: (1) Both ozone flux and dry deposition velocity were characterized by strong diurnal variation, with daily mean values of －0.40 μg?m-2?s-1 (minus sign refers the direction towards the ground) and 0.55 cm/s respectively.(2) The ozone dry deposition flux is significantly influenced by the topographic wind, and the maximum ozone dry deposition flux occurs during the valley-wind prevailing period (0900－1500 LST) with a mean value of －0.67 μg?m-2?s-1, and it comes to averagely －0.44 μg?m-2?s-1 over the mountain-valley wind shift period (0800 LST in the morning and 1600 LST in the afternoon). When the observation site is predominated by mountain breeze, the downward ozone flux decreases to only －0.26 μg?m-2?s-1. The ozone dry deposition velocity displays the same feature with mean values of 0.74 cm/s, 0.50 cm/s, 0.47 cm/s respectively for these periods.(3) Canopy resistance calculated with the resistance model indicates the mean value of 184.0 s/m for the whole observation period. During the daytime, due to the gas-phase exchanges near leaf stomata and the strong photosynthesis effects, canopy resistance (109.0 s/m) is lower than that at night (217.7 s/m) when the plant physiological activities drop off.