Serum collected from 68 thick-billed parrots (Rhynchopsitta pachyrhyncha) from 15 institutions was analyzed for ionized Ca (iCa), total Ca (tCa), P, total protein (TP), albumin (Alb), parathyroid hormone (PTH), and vitamin D₃. Values were not distributed normally; 95% frequency intervals were as follows: iCa (0.82–1.3 mmol/L), tCa (1.37–2.09 mmol/L,), P (0.35–1.75 mmol/L), TP (21–39 g/L), Alb (9–13 g/L), PTH (0–65.68 pmol/L), and vitamin D₃ (5.2–51 nmol/L). Sixty percent (±7.5%) of tCa was ionized. Female thick-billed parrots had significantly higher mean iCa (1.11 mmol/L, n = 22) than male thick-billed parrots (1.05 mmol/L, n = 32). tCa and iCa values in thick-billed parrots were lower than the reported values for other psittacine species. A significant positive linear relationship existed between Alb–TP and iCa–tCa ratios. A significant inverse linear relationship was also identified between the tCa–P ratio and PTH. These findings are consistent with known domestic avian Ca physiology.