The adsorption of formaldehyde (HCOH) molecule on the pristine and silicon-doped (Si-doped) single-walled (8,0) boron nitride nanotubes (BNNTs) is investigated using density functional theory (DFT) calculations. Compared with the weak physisorption on the pristine BNNT, the HCOH molecule presents strong chemisorption on both silicon-substituted boron defect site and silicon-substituted nitrogen defect site of the BNNT, as indicated by the calculated geometrical structures and electronic properties for these systems. It is suggested that the Si-doped BNNT presents high sensitivity to toxic HCOH. Based on calculated results, the Si-doped BNNT is expected to be a potential novel sensor for detecting the presence of HCOH. (C) 2008 Elsevier B.V. All rights reserved.