Here, we employed first-principles calculations to investigate the structure, stability and electronic properties of ultra-thin BC2N nanotubes. We obtained a novel, screwy, helicoidal and cyclical (as the structure of DNA molecule) structure that had not been reported in previous studies. Further, we found the stability of ultra-thin BC2N nanotubes depends on not only the number of B-N bonds but also the arrange modes of CNT and BNNT segments. Our results also showed the electronic properties of ultra-thin BC2N nanotubes are tunable and abnormal when compared to the relative big ones. (C) 2014 Elsevier B.V. All rights reserved.