(1Faculty of Agriculture and Biotechnology, Yunnan Agricultural University, Kunming, 650201 Agricultural Research Institute, Academy of Yunnan Tobacco Science, Yuxi 653103) Abstraction of the high molecular weight (HMW) DNA is one of the key steps in construction of a bacterial artificial chromosome (BAC) library. Two methods （Once selection and twice selection）are tried for abstraction of high molecular weight nuclear DNA from tobacco. Although the concentration of the HMW DNA was lower with the twice selection method, more and purer plugs could be yielded. In addition, the twice selection used less materials. Therefore, the method was better than the once selection method.
