The interest of consumers, as well as the food and feed industry in legumes is constantly increasing. However, the use of legume seeds is limited by the fact that they contain various non-nutritive compounds such as raffinose family oligosaccharides (RFOs). On the other hand, RFO compounds are considered prebiotic substances improving health and growth of organisms. Our study consisted in the long-term monitoring of RFO contents in seeds of several legumes cultivated in Poland. The seeds of pea (25 cultivars), faba bean (5 cultivars), and lupins (41 cultivars) were harvested between 2013 and 2019, whereas soybean seeds (27 cultivars) were harvested between 2015 and 2019. The analysis showed that the content of RFOs in soybean seeds ranged from 33.75 to 69.30 mg per g dry matter (DM), 57.23 to 130.38 mg/g DM in lupin seeds – 52.03 to 80.60 mg/g DM in pea seeds, and from 32.15 to 65.17 mg/g DM in faba bean seeds. Yellow lupin seeds had the highest total RFO contents in DM, whereas faba bean and soybean seeds showed the lowest RFO contents. Stachyose was the dominant oligosaccharide in all soybean and lupin seeds, while verbascose was the dominant oligosaccharide in most pea and faba bean seeds. Some pea cultivars contained more stachyose than verbascose. Crop species, cultivar, growing environment, and processing methods determine the suitability of individual seeds for the feed and food industry.