The objective of the study was to evaluate the effects of oral calcium formate supplementation on serum total calcium (tCa), ionic calcium (iCa), NEFA, BHBA, cholesterol, AST, albumin, P and Mg minerals in early lactation cows. In a commercial dairy farm with 950 lactating cows in Southern Brazil, 129 Holsteins (45 primiparous and 84 multiparous) were blocked by parity and by tCa status (Idexx VetTest Chemistry Analyzer) 6 h after calving. Blood samples were analyzed for group allocation (normal and hypocalcemia groups) using 8.2 mg/dL (2.05 mM) as the cutpoint. Within each block, fresh cows were randomly allocated to 3 groups; control (C), group 1 (G1), and group 2 (G2), respectively supplemented with 0, 350 and 700 mL of 14.3% (wt/wt) calcium as a 48.6% aqueous suspension of calcium formate (Calfon Oral, Bayer Animal Health), 6 h after parturition. Eight blood samples were collected on evacuated tubes without anticoagulant, 6 (t1; just before the oral calcium supplementation), 6.5 (t2), 7.0 (t3), 7.5 (t4), 8.0 (t5), 10 (t6), 14 (t7), and 24 (t8) h after calving. Serum samples were frozen at −80°C for 90 d and then analyzed for tCa using colorimetric test (Arsenazo) and by ion selective electrode (iCa). Data were analyzed using the MIXED procedure of SAS with a model containing the effects of block, treatment, time, and treatment × time interaction as fixed effects and cow within treatment as a random effect. Hypocalcemia incidence rates were 37% using on-farm tCa from VetTest (≤2.05 mM), 40% using tCa (≤2.0 mM) and 71% using iCa (<1.0 mM). The lowest tCa and iCa values were observed at 24 h postpartum. It has shown an increase (P < 0.05) in serum levels of iCa and tCa between t2 to t7 for G1 and G2 compared with group C. Oral Ca supplemented cows have shown higher (P < 0.05) AST concentrations at t4 to t8 and lower (P < 0.05) Mg levels at t5 to t8. No differences were detected (P > 0.05) for the remaining analytes. The oral calcium formate supplementation has shown beneficial effects on the increment of ionic and total Ca on early lactation dairy cows, important goals to control metabolic disorders in dairy farms.