Total 208 day-old female broilers were fed on isonitrogenous and isoenergetic diets containing seeds of sweet narrow-leafed (L. angustifolius cv. Bojar – NL) or sweet yellow (L. luteus cv. Parys – YL) lupin at the level of 0 (control, C), 10% (days 1–14), and 15% or 25% (days 15–35 of life). The diets were fed unsupplemented or supplemented with mannanase. At the end of second week of life, the birds fed both lupin diets were smaller than control birds, due to lower feed intake (P < 0.05). The final body weight (P < 0.05) and body weight gain (P < 0.01) in birds fed the NL were higher than in those fed the YL diets due to higher (P < 0.01) feed intake, but their feed conversion ratio was worse (P < 0.01). The higher dietary lupin level did not affect feed intake, but depressed feed utilization. The relative liver weight was greater in birds fed YL than NL. The viscosity of ileal digesta in birds fed the NL diets averaged 3.12 mPas.s and was significantly greater than in control and YL-fed birds. Villi height and crypt depth were lower (P < 0.05) at the increased level of dietary lupin. The dietary treatments did not affect the total short-chain fatty acid concentration in ileal and caecal digesta. Mannanase supplementation did not significantly affect any of the measured parameters, but increased the butyrate concentration in caecal digesta (P < 0.05). Inclusion of sweet lupin at a 15% level can be accepted in older broiler diets provided with adequate amino acid and fat supplementation.