This paper presents the course of alder pollination season in Poland in 2020. The measurements were performed in Bydgoszcz, Bialystok, Lublin, Olsztyn, Opole, Piotrkow Trybunalski, Sosnowiec, Szczecin, Warsaw, Wroclaw and Zielona Gora. Volumetric method with the use of Volumetric Spore Trap (Burkard, Lanzoni) was implemented. Pollen season was defined as the period in which 95% of the annual total catch occurred. The alder pollen season in 2020 started about 10–30 days earlier compared to 2017–2019. The pollen season started first in Szczecin, Opole and Zielona Gora (in the second half of January). In the other cities alder pollen season started in first half of February. The highest daily pollen count was recorded in Lublin (1211 P/m3). In other cities the maximum concentrations ranged from 160 P/m3 in Sosnowiec to 465 P/m3 in Piotrkow Trybunalski. The highest alder pollen concentrations were detected in the first decade of March (March 1st–3rd). Only in Zielona Gora, Wroclaw, Opole and Sosnowiec the maximum concentration was recorded in the third decade of February. The annual pollen sum of Alnus in 2020 was even 5–10 times lower than in years 2019.