The assessment of the fluctuating asymmetry based on measurement of the parameters of left and right parts of silver birch (Betula pendula (L.) Roth.) leaves and relative sizes of pairs of Scots pine (Pinus sylvestris L.) needles from the Chernobyl Exclusion Zone (ChEZ) was carried out. Twelve samples of both birch leaves and pairs of needles were collected from 10 trees at 5 sites in the Chernobyl Exclusion Zone and also at one control site located outside the ChEZ. Values of gamma dose rate in the air varied between the sites from 0.1 to 40 μGy h−1. Activity concentrations of 90Sr and 137Cs in the birch leaves varied over the range of 0.9÷2460 kBq kg−1 and 0.1÷339 kBq·kg−1 (DW), respectively. In addition to the above, in the Scots pine needles, these ranges were 0.7 ÷1970 kBq kg−1f for 90Sr and 0.1÷78 kBq kg−1 (DW) for 137Cs. From the values of the radionuclides activity concentrations in the plants, the internal dose rate is estimated to be in the range of 0.1 ÷ 274 μGy h−1. The main sources of the internal dose rate were radiation of 90Sr and 90Y. Indices of fluctuating asymmetry of silver birch leaves and Scots pine needles varied over the range of 0.048 ± 0.007 ÷ 0.060 ± 0.009 and 0.014 ± 0.002 ÷ 0.018 ± 0.002, respectively, and did not statistically differ for all experimental sites. The indices also did not depend on the external or internal dose rate of ionizing radiation for plants. The above findings seem to be consistent with other research effort in terms of understanding the response of organisms to chronic pollutant exposure and the long-term effects of large scale nuclear accidents. Display omitted •30-year impact of Chernobyl on plant species development.•Fluctuating asymmetry (FA) used as a measure of developmental stability.•No changes in developmental stability along gradient of a dose rate.•FA of leaves and needles remains unchanged in the face of the ionizing radiation.