In order to provide the references for appropriate construction and protection of urban green system and reliable prevention and control of tropic pollinosis, the seasonal dynamics of species and quantity of airborne pollens were investigated in Beijing urban area. With a Burkard volumetric trap, airborne pollens were sampled from December 31st 2010 to December 31st 2011. Through the whole year of 2011 the total quantity of pollens amounted to 136 858 grains, and the pollen dispersion period lasted 213 days from March 20^th to October 18^th, accounting for 58% of the year. Two peaks of pollen concentration in air were observed, which happened from March to April and from August to September. In the spring peak, the major airborne pollens were tree pollens such as Oleaceae, Populus and Salix pollens, accounting for as much as 30% of the total annual pollen amount. While in the autumnal period, weed pollens such as Artemisia, Chenopodiaceae and Amaranthaceae pollens made up the second peak of pollen air concentration, and the amount of pollens accounted for 50% of the annual total value. In summer, the blooming flowers were generally entomophilous while in winter the plants and the flowers seared, resulting in low values of airborne pollen concentration in these periods. The results also indicated that the airborne pollens caught in autumn were of high allergenicity, which caused a high incidence of tropic pollinosis in autumn, with a peak from August to September and 95% of the patients with obvious symptoms recorded in this period. The composition of airborne pollens changed considerably compared with the reported pattern in 1980s, which might be attributed to extensive construction of parks, roads and communities in the past 30 years. It was further suggested that the dispersion characters and air concentration of pollen were largely determined by local vegetation and climatic condition. The results and findings of this investigation can provide reliable data for protection and treatment of tropic pollinosis as well as the varieties choice of city plants.