We succeeded in the crystallization of d(CGCGCG)(2) and methylamine Complex. The crystal was clear and of sufficient size to collect the X-ray crystallographic data up to 1.0 angstrom resolution using synchrotron radiation. As a result of X-ray crystallographic analysis of 2F(o)-F-c map was much clear and easily traced. It is the first time monoamine co-crystallizes with d(CGCGCG)(2). However, methylamine was not found from the complex crystal of d(CGCGCG)(2) and methylamine. Five Mg ions were found around d(CGCGCG)(2) molecules. These Mg ions neutralized the anion of 10 values of the phosphate group of DNA with five Mg2+. DNA stabilized only by a metallic ion and there is no example of analyzing the X-ray crystal structure like this. Mg ion stabilizes the conformation of Z-DNA. To use monoamine for crystallization of DNA, we found that we can get only d(CGCGCG)(2) and Mg cation crystal. Only Mg cation can stabilize the conformation of Z-DNA. The method of using the monoamine for the crystallization of DNA can be applied to the crystallization of DNA of long chain of length in the future like this. (c) 2006 Elsevier Inc. All rights reserved.