Background: Decreased plasma essential amino acid (EAA) levels, increased nonessential amino acid (NEAA) levels, and low EAA to NEAA ratio (E/NEAA) are common in peritoneal dialysis (PD) patients and may impact uremic complications. In the present study, we investigate the impact of keto acids-supplemented lowprotein (sLP) diet on plasma amino acids (AAs) patterns in stable PD patients. Methods: This is a supplemental analysis of a previously published prospective and randomized trial. Thirty-nine PD patients selected from the original population were divided to receive either low (LP: 0.6-0.8 g/kg ideal body weight [IBW]/d, n = 13), keto acids-supplemented low-(sLP: 0.6-0.8 g/kg IBW/d + 0.12 g/kg IBW/d of keto acids, n = 12), or high-(HP: 1.0-1.2 g/kg IBW/d, n = 14) protein diets and followed for 1 year. Plasma AA patterns were assessed at baseline and 12 months using high-performance liquid chromatography. Results: Whereas there were no significant differences between the three groups at baseline, following 12 months, the E/NEAA had increased significantly in group sLP (0.58 ± 0.16 to 0.83 ± 0.20, p < 0.05), but was not different in either LP (0.62 ± 0.20 to 0.72 ± 0.13, p = ns) or HP (0.66 ± 0.14 to 0.74 ± 0.12, p = ns) group. This change in E/NEAA in group sLP was due to a significant decrease in NEAA concomitantly with maintained EAA levels, whereas in the other two groups, neither EAA nor NEAA changed significantly. Conclusions: A low-protein diet supplemented with keto acids significantly improved the pattern of plasma AA in prevalent PD patients.