The bachelor thesis deals with radiocaesium activity in the fruit of bilberry. Radiocaesium 137Cs entered the environment only recently as a result of tests of nuclear weapons and nuclear power plants accidents. In view of the relatively long half-life, we can still detect radiocaesium in environmental compartments, especially in the forest ecosystem. Bilberry (Vaccinium myrtillus L.) is a reference material for accurately determining radiation contamination because of its ability to effectively accumulate radioactivity. The aim of this work was to analyse the environmental contamination with emphasis on the content of 137Cs in mountain areas and the behaviour of 137Cs in the soil - plant - fruit system. To process the sampling methodology and sample processing methodology for gamma spectrometric analysis and perform sampling, processing, sample analysis, and evaluation of the results. To calculate the aggregated transfer factor and the effective dose of the population from the consumption of the fruits from the obtained results. Sampling was carried out in central Slovakia at locality Flochová. Samples of vegetative and generative plant organs and soil samples were collected. Radioactivity was determined by gamma spectrometry, using a HPGe semiconductor detector and a NaI(Tl) scintillation detector. Fruit dry matter exhibited a mass activity 126.3 ± 7.2 Bq.kg-1 and fresh fruits 16.7 ± 1.0 Bq.kg-1. The soil sample calculated surface area activity was 2373 ± 132.9 Bq.m-2. Aggregated transfer factor from soil to fruit has been estimated to be 5.3.10-2 m2.kg-1. Consumption of 0.61 kg of fruit from the investigated locality contribute to the annual dose of ionizing radiation of the population from natural sources with 1.32.10-4 mSv.