High mobility group box protein-1 (HMGB-1) was recently identified as a new type of inflammatory cytokine. Inflammation can lead to malnutrition to some extent. Our study was aimed to clarify the relationship between serum HMGB-1 level with microinflammatory state and nutritional status in continuous ambulatory peritoneal dialysis (CAPD) patients. Patients in the treatment of maintenance of peritoneal dialysis for >6 months were included. HMGB-1, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) were measured by enzyme-linked immunosorbent assay (ELISA). High-sensitivity C-reactive-protein (hs-CRP), prealbumin (PA), serum albumin (S-Alb), hemoglobin (Hb), subjective global nutritional assessment (SGA), and CAPD presents' urea clearance rate (Kt/V), creatinine clearance (CrCl), residual glomerular filtration rate (rGFR), and dialysate-to-plasma ratio of creatinine after 4 h (D/P(4Cr)) were analyzed. The Independent-samples t test and Pearson's rank correlation test were used. Serum HMGB-1, IL-6, and TNF-α of CAPD patients were significantly higher than in the control group (P < 0.05); Serum HMGB-1 levels had positive relationships with TNF-α (r = 0.730, P < 0.01), hs-CRP (r = 0.361, P < 0.01), and IL-6 (r = 0.865, P < 0.01), and had negative relationships with Hb (r = -0.59, P < 0.01), Alb (r = -0.34, P < 0.05), and PA (r = -0.44, P < 0.01); no significant relationships were found between serum HMGB-1 with SGA, peritoneal dialysis age, Kt/V, CrCl, rGFR, and D/P(4Cr). Our study revealed that HMGB-1 was elevated significantly in CAPD patients and correlated with indicators of inflammation and malnutrition. Serum HMGB-1 could be used as a marker for evaluating inflammation and malnutrition in CAPD patients.