We tested the hypothesis that low vitamin D receptor (VDR) level causes intestinal vitamin D resistance and intestinal calcium (Ca) malabsorption. To do so we examined vitamin D regulated duodenal Ca absorption and gene expression (TRPV6, 24-hydroxylase (CYP24), calbindin D_9k (CaBP) mRNA and CaBP protein) in wild-type mice (WT) and mice with reduced tissue VDR levels (i.e. heterozygotes for the VDR gene knockout, HT). Induction of CYP24 mRNA levels by 1,25 dihydroxyvitamin D₃ (1,25(OH)₂ D₃) injection was significantly reduced in the duodenum and kidney of HT mice in both time course and dose response experiments. TRPV6 and CaBP mRNA levels in duodenum were significantly induced after 1,25(OH)₂ D₃ injection but there was no difference in response between WT and HT mice. Feeding a low calcium diet for 1 week increased plasma PTH, renal 1 hydroxylase (CYP27B1) mRNA level, and plasma 1,25(OH)₂ D₃ and this response was greater in HT mice (by 88%, 55%, and 37% higher, respectively). In contrast, duodenal TRPV6 and CaBP mRNA were not higher in HT mice fed the low calcium diet. However, the response of duodenal Ca absorption and CaBP protein to increasing 1,25(OH)₂ D₃ levels was blunted by 40% in HT mice. Our data show that low VDR levels lead to resistance of intestinal Ca absorption to 1,25(OH)₂ D₃ and this resistance may be due to a role for the VDR (and VDR level) in the translation of CaBP.