Based on the Beijing 325m meteorological tower,the concentration of O₃ and NOx and corresponding meteorological elements such as temperature,wind and humidity were measured in the urban atmospheric boundary layer in the July and August of 2002.Analysis results show that in summer O₃ has remarkably diurnal variation in the boundary layer in Beijing city and the concentration of O₃ increases with height;most of O₃’s diurnal variations are mono-peak pattern,and double-peak pattern only occurs in lower levels;the concentrations of O₃ and temperature reach the peak at the same time or O₃ lags a little.