The study aims to compare the oak pollen season in selected Polish cities: Bialystok, Bydgoszcz, Cracow, Katowice, Piotrkow Trybunalski, Lublin, Olsztyn, Opole, Szczecin, Warsaw, and Wroclaw in 2020. Measurements were made using the volumetric method, with a Hirst-type sampler. Oak pollen season, defined as the period with 98% of the annual total catch, started between April 14th (in Opole) and April 25th (in Lublin). The season ended on June 1st at the latest; in Sosnowiec, Bydgoszcz, Olsztyn, and Bialystok. It lasted from 30 to 47 days (37 days on average). The maximum daily oak pollen concentrations were observed between April 24th and May 11th. The highest annual sum of oak pollen grains (SPI) was recorded in Lublin, while the lowest in Bialystok. The highest concentrations of 596 oak pollen grains/m3 were noted in Lublin on April 28th. The longest exposure to high concentrations of oak pollen (> 91 grains/m3), lasting 12–13 days, was recorded in Lublin, Opole, and Wroclaw.