Twenty-four intact male Bonga lambs were studied in a 100-day experiment to evaluate the effect of feeding tannin rich leaves of Albizia gummifera (AG) on nutrient utilization, growth performance, and carcass composition. The dietary treatments consisted of hay alone (T1, control), AG at 30 % of control diet + T1 (T2), and T2 + polyethylene glycol 6000 (PEG) (T3, 40 mg PEG, 1 kg AG/head on a dry mass (DM) basis. The lambs were individually fed at 50 g DM/kg live weight. In the last 10 days of the experiment, all animals from each treatment were harnessed with feces collection bags. At the end of the experiment, lambs were slaughtered after overnight fasting for measurements of carcass characteristics. Crude protein, neutral detergent fiber, and condensed tannin contents of AG were 300, 586, and 108 g/kg DM, respectively. Lambs fed AG with PEG had higher (P < 0.001) feed intake, digestibility, carcass weight, and weight gain compared with other treatments. Although lambs fed diet T2 were able to utilize AG, the efficiency of its utilization was lower (P < 0.001) than the PEG-treated groups. The improvement in nutrient intake and digestibility, carcass weight, and growth performance of lambs supplemented with PEG emphasizes the negative effect of tannins on livestock performance. Leaves of AG enhance digestibility and performance in tropical hay-fed sheep, and the addition of PEG further improves this effect, likely due to the binding of tannins.