Phenolic compounds play an important role among plants and in human nutrition. The content of phenolic compounds depends on the plant species, the nutrient content of the soil, climatic conditions, parasites and the age of the plant. Buckwheat is considered as a plant with a high content of phenolic compounds. The purpose of the master's thesis was to study how the content of phenolic compounds in individual parts of buckwheat changes during growth, which was followed in the samples of leaf and flower of the type of buckwheat F. esculentum Darja and to compare the content of phenolic compounds in leaf, flower and fruit samples of different buckwheat species that grew under the same conditions. We analyzed eight species of buckwheat: F. esculentum, F. cymosum, F. giganteum, F. gracilipes, F. leptopodum, F. rotondatum, F. tataricum and F. urophylum. For some species we had several sub-species. To determine the content of total phenolic compounds and total flavonoids, one of the most widespread groups of phenolic compounds in nature, spectrophotometric methods with Folin-Ciocalteu reagent and aluminum chloride were used. Individual flavonoids, such as quercetin, quercitrin and rutine, were determined by the HPLC method. Using the Pearson correlation coefficient in the Excel program, we concluded that the methods correlated well and yielded comparable results. In flower samples of F. esculentum Darja the content of studied compounds increased to a certain degree of growth, then decreased, while the content in leaf samples increased unevenly. In flower samples, the highest measured value of total phenolic compounds was 124 mg/g of dry drug, of total flavonoids 112 mg/g of dry drug, of rutine 77.1 mg/g dry of drug, of quercitrin 29.7 mg/g of dry drug, quercetin was only detectable in traces. In leaf samples, the highest measured content of total phenolic compounds was 117 mg/g of dry drug, of total flavonoids 107 mg/g of dry drug, of rutine 83.7 mg/g of dry drug. Quercitrin and quercetin were detectable only in traces. By analyzing different buckwheat species, leaf samples of F. tataricum and F. rotondatum and flower samples of F. leptopodum consistently showed a high content of phenolic compounds. With the highest contents, leaf samples of F. cymosum asklepios (total phenolic compounds: 155 mg/g of dry drug, flavonoids: 143 mg/g of dry drug, rutine: 96.5 mg/g of dry drug) and flower samples of F. giganteum 1978 (total phenolic compounds: 78.1 mg/g of dry drug, flavonoids: 77.8 mg/g of dry drug, rutine: 64.9 mg/g of dry drug) were particularly prominent. Phenolic compounds were present in leaves and flowers at a higher concentration than in fruits. In the master's thesis we confirmed that the age of buckwheat, plant parts and genetics affect the content of phenolic compounds.