The effects of A. nilotica (tannin-rich plants) on the digestion coefficient of nutrients and its antibacterial properties were "in-vivo" investigated in this study. Twenty five male baladi goats aged 3-4 years and weighing 19-21 kg were randomly classified into five groups (5 per each). Each animal group was fed on one of the experimental diets containing different levels of A. nilotica leaves (0%, 5%, 10%, 15% & 20%). Chemical analysis of A. nilotica leaves revealed that its content of crude protein, crude fiber, ash were 12.1%, 30.5%, 13.2%, respectively, while the total soluble tannins were 34%. The digestion coefficient of dry matter (DM), crude protein, crude fiber and nitrogen free-extract (NFE) in the control group were better than those of the experimental diets. However, digestion coefficient of most nutrients were significantly decreased (P < 0.01) with increasing levels of A. nilotica in the goat's diets. Absorbed and retained nitrogen (g/day) were decreased with increasing levels of A. nilotica. Concerning nitrogen balance, all animals of the experimental groups showed positive nitrogen balance. Colony forming units (CFU) were drastically reduced in both faecal und ruminal juice samples. This reduction was directly proportional to levels of A. nilotica in the ingested feed. The CFU were reduced in the faecal samples from 5.9 x 10(8)/g (control group) to 2.8 x 10(4) (fifth group) (that received 20% Acacia nilotica). On the other hand, the CFU/ml of ruminal juice samples were reduced from 5.8 x 10(6) (control group) to 1.8 x 10(3) (fifth group). On the other hand, Cl. perfringens count was reduced from 1.0 x 10(4) to 6.3 x 10/g in the faecal samples while their count was reduced from 6.2 x 10(2) to 4.4 x 10/ml in case of ruminal samples. The reduction of total bacterial and Cl. perfringens counts were directly proportional to the levels of A. nilotica in the diets of goats.