The results of measurement of atmospheric radon concentration in Beijing, China, are reported. Continuous observation was performed hourly throughout 2003 to provide data on annual average radon concentration as well as the variation of radon concentration. An arithmetic annual mean value of 14.1 +/- 5.5 Bq m(-3) was obtained. The value was slightly higher than the world average and the national average. For the monthly average radon concentration, the maximum was 18.5 +/- 5.0 Bq m(-3) in November, while the minimum was 9.9 +/- 4.1 Bq m(-3) in May. Diurnal variation was also observed, and the average daily pattern of radon concentration consisted of a minimum in the late afternoon and a maximum in the early hours of the morning.