Molecular‐dynamics simulations of amyloid‐β_1–42 peptides including D‐aspartic acid residues were performed, and their three‐dimensional structures were compared. The simulations were performed in an aqueous environment using a continuous solvent model. In the structures obtained from simulations, the occurrence ratio of β‐extended structures for the peptide that included D‐Asp23 was larger than that for the wild‐type peptide. These β‐extended structures appeared in the C‐terminal region of the peptide, and the α‐helix structures of the region were lost. On the other hand, for the peptide that included the stereo‐inverted form of Asp1 as well as D‐Asp23, the occurrence ratio of β‐extended structures in the C‐terminal region was lower than that of the peptide including only D‐Asp23.