Background: Vitamin D deficiency is associated with a higher risk of mycobacteria infection. Little information is available on the vitamin D metabolism in the nontuberculous mycobacteria (NTM) infection. Antimicrobial peptide is immunomodulatory peptide that has pleiotropic effects and is regulated by vitamin D. We aimed to determine the association factors of the vitamin D metabolism in patients with NTM lung disease.Methods: 25–hydroxyvitamin D (25[OH]D), antimicrobial peptide cathelicidin (LL–37), antimicrobial peptide defensin (hBD–2), and vitamin D binding protein (DBP) of sera from 82 patients with NTM lung disease and 28 control subjects were analyzed. Quantitative, real-time reverse-transcriptase–polymerase-chain-reaction (RT–PCR) assays were used to confirm the relative expression of cathelicidin gene (CAMP), defensin gene (DEFB4), vitamin D receptor (VDR), and 1α–hydroxylase (CYP27B1) mRNA in immune cells of study subjects. The patients with NTM lung disease had infections as follows: Mycobacterium avium 30%, M. intracellulare 29%, M. abscessus 20%, and M. massiliense 21%. Results: There were all female and the median age was 57 years old in patient group and 60 years old in control group. The patients with NTM lung disease were leaner than controls (body mass index, 20.5 kg/m2 (19.1–21.9) vs. 23.9 kg/m2 (22.1–24.5), p