AbstractFour substituted thienyl chalcone derivatives: 3‐(4‐chlorophenyl)‐1‐(3‐thienyl)‐2‐propen‐1‐one (CTC) (HE Youping et al. 1994), 3‐(4‐bromophenyl)‐1‐(3‐thienyl)‐2‐propen‐1‐one (BTC) (HE Youping, SU Genbo 1995 (b)), 3‐(4‐methylphenyl)‐1‐(3‐thienyl)‐2‐propen‐1‐one (MTC), and 1,3‐Di(2‐thienyl)‐propen‐1‐one ((DiTC*) (LI Zhengdong, SU Genbo) have been synthesized. Analysis of these crystal structures showed to form noncentrosymmetric structure, CTC and BTC crystals belong to the space group P21, MTC belong to Cs, its isomer (MTC*) (HE Youping, SU Genbo 1995(a)) and isomer (diTC*) of DiTC(T‐1) (GOTOH, HAHASHI) were crystallized in the centrosymometric space group P21/n (LI Zhengdong, SU Genbo; HE Youping, SU Genbo 1995(a)). CTC, BTC, and MTC showed high SHG activity 90 to 100 times as large as KDP and also b