Chemical composition plant parts (roots, stalks, leaves, blossoms) of common buckwheat (Fagopyrum esculentum Moench) and selected products made from its seeds (peels, whole seed, wholemeal flour, broken seeds, crunchy products Natural and Cocoa, flour, and pasta) was determined. Samples were dried and ground to a fine powder. All analyses were performed according to the Commission Regulation no. 152/2009, while rutin concentration was determined by the modified HPLC method. The lowest content of moisture was found in roots (4.3%) and in peels (almost 8%) and the highest moisture (nearly 11%) was discovered in seeds. The lowest amount of crude protein (3.5%) was found in peels, the highest crude protein amount (>13%) in both flours and leaves (23%). The starch content (>50% in dry matter) differs from one sample to another. Only in peels the content of starch was about 3.5%. From all examined samples, the lowest content of fat was found in crunchy products Cocoa, 1.7%. The lowest amount of histidine was determined in all studied samples, except peels, the highest content of glutamic acid was determined in almost all samples, except peels. Whole-meal flour is very rich source of Ca and Fe. The content of these elements was 1172 mg.kg-1 and 45.9 mg.kg-1, respectively. On the other hand, the highest content of Pb (>1 mg.kg-1) was found in broken seeds. The greatest concentration of rutin was determined in blossoms and leaves (83.6 and 69.9 mg.g-1), respectively. On the other hand, the lowest concentrations of rutin were found in buckwheat products (generally less then 1 mg.g-1, i.e. in wholemeal flour, 702 μg.kg-1, the lowest almost 10 μg.kg-1) in pasta.