The intestinal absorption of calcium (Ca) from Ca ascorbate (Ca-AsA) was investigated in normal rats. Each animal was perorally administered either 5 mg (low dose) or 10 mg (high dose) of Ca in 1 ml of distilled water as Ca-AsA, Ca carbonate (CaCO₃), or Ca chloride (CaCl₂), which were intrinsically labeled with ⁴⁵Ca using ⁴⁵CaCl₂. The amount of radioactivity in plasma was measured periodically up to 34 h after dosing, and pharmacokinetic parameters were calculated from the radioactivity in plasma. The time taken to reach the maximum ⁴⁵Ca level (T_max) did not differ among the three groups. The area under the plasma ⁴⁵Ca level/time curve (AUC∞) value for the Ca-AsA group was significantly higher than those for the CaCO₃ and the CaCl₂ groups. The radioactivity at T_max (C_max) for the Ca-AsA group was significantly higher than those for the CaCO₃ and the CaCl₂ groups for the low dose, and comparable with or significantly higher than those for the CaCl₂ and CaCO₃ groups for the high dose. Similar results were observed for whole-body ⁴⁵Ca retention. Radioactivity in the femur 34 h after dosing was the highest in the Ca-AsA group and the lowest in the CaCO₃ group. The rank order of solubility in water, the first fluid (pH 1.2, JP-1) of JPXIII disintegration medium, acetate buffer solution (pH 4.0), triethanolamine-malate buffer solution (pH 7.0) and ammonium chloride buffer solution (pH 10.0) at 37°C was CaCl₂ > Ca-AsA > CaCO₃. In contrast, the rank order of the solubility in the second fluid (pH 6.8, JP-2) of JPXIII disintegration medium at 37°C was Ca-AsA > CaCl₂ > CaCO₃. These results indicate that the absorbability of Ca from Ca-AsA is almost comparable with, or higher than, that from CaCl₂ and significantly higher than that from CaCO₃ because of its high degree of solubility in the intestine. Therefore, Ca-AsA would be useful as a Ca supplement with relatively high absorption from intestine.