Abstract: Because the formal English name for the univalent radical derivatized from thiophene,namely thienyl,is not simply generated from its parent thiophene according to the nomenclature rules of IUPAC,it is very easy for people to misuse word thiophenyl in place of thienyl,just as thiophenyl is derivatized from the parent thiophene according to one of the IUPAC principles that the vowel suffix e of a parent name is substituted by yl to yield its univalent substituent name via thiophene→thiophen→thiophenyl.Since the name thiophenyl has been customarily employed to represent PhS (i.e.,phenylthio),it can't be used to designate thienyl substituent any longer and the word thienyl is the only official nomenclature for the univalent radical of thiophene as a substituent.All the chemistry workers must take extremely care to prevent the misusage of thiophenyl when they want to express their meaning of thienyl.

Key words: thienyl, IUPAC nomenclature principle, thiophenyl (PhS)