1-Methyl-4-2-[4-(dimethylamino)phenyl]ethenyl}pyridinium p-toluenesulfonate and p-chlorobenezenesulfonate (DAST and DASC) have excellent second-order nonlinear optical properties, and they can generate high-power and broadband terahertz waves by difference frequency generation. However, the output power becomes weak at some frequencies where inherent absorption of crystals exists. Thus, we prepared mixed crystals of DAST and DASC since their crystals are isomorphous. Properties of mixed crystals were almost an average of DAST and DASC, and the minimum terahertz-wave generation intensities could be increased especially in the region where the absorption peak positions were different between two compounds. (c) 2007 Published by Elsevier B.V.