Abstract: The aim of this study was to compare the accuracy of endogenous ileal amino acid loss values determined by regression (REG) method, the protein-free (PF) method and the homoarginine (HA) method. The endogenous ileal amino acid flows of growing swine determined using above methods were used to correct the apparent ileal amino acid digestibility (AID), and then judge the accuracy of endogenous ileal amino acid values by stability of collected digestibility values with the change of dietary protein concentration. Six barrows, with an initial body weight of 28 kg, were surgically fitted with simple T-cannulae at the distal ileum and fed six experimental diets containing crude protein 0, 5%, 10%, 15%, 20%and 25% according to a 6 × 6 Latin-square design. Each experimental period lasted 8 days. On day 6 of each period, ileal digesta wascontinuously collected for 24 h to determine AID and standardized true ileal amino acid digestibility (STID) using PF method. On day 8, the pigs were given a single meal of the HA diets and their ileal digesta was collected for 24 h in order to determine the HA flow and calculate real ileal digestibility (RID). The results showed that the values of endogenous ileal amino acid flow except glycine and proline determined using REG method were lower than those using PF method (P<0.1). Comparing with the HA method, PF method underestimated the loss of endogenous ileal amino acids (P<0.01) in the range of 10%- 25% of dietary protein concentration. The AID for all essential amino acids except phenylalanine and valine showed a quadratic increase (P<0.05) with an increase in dierary protein. And STID decreased (P<005) linely or quadraticly with an increase of dietary protein level. However, RID was stable and not influenced (P>0.05) by dietary protein level within 20% of CP. In conclusion, REG method and PF method underestimated the loss of endogenous ileal amino acids and HA method was more accurate than REG or PF method for determining endogenous ileal amino acid loss.