The growth and physiological responses of the rats to diet supplemented with raw and-fermented yellow and blue lupin seeds were determined. The diets containing soya bean meal, raw and fermented blue and yellow lupin were administered to eight rats in each diet group for four weeks. Yellow lupin seeds in the diets of rats improved significantly (p<0.05) feed intake, protein digestibility, body mass gain and protein efficiency ratio in comparison with blue lupin seeds. On the contrary, blue lupin seeds affected significantly (p<0.05) gastrointestinal fermentation processes in comparison with yellow lupin seeds. Fermentation of lupin seeds increased crude protein content and reduced phytate and oligosaccharide content. In the fermented products, a higher number of lactic acid bacteria and yeasts but reduced number of coliform bacteria was found. Fermentation bypositively (p<0.05) affected protein digestibility of feed, body mass gain and protein efficiency ratio of rats, as well as the activity of some bacterial enzymes and cholesterol concentrations in the blood serum.