We have investigated the origin of methane/hydrogen RIE (reactive ion etching)-induced damages. ZnSe and ZnCdSe/ZnSe-based quntum well wires with wire widths ranging from 1000 nm to 20 nm have been fabricated by electron-beam lithography and a methance/hydrogen RIE. Photoluminescence (9.5 K) is used for the study of the causes of RIE-induced damage. The results indicate that the RIE-induced damage lead to the red shift of peak emission. From PL data of ZnSe wires, we concluded that RIE-induced damage causes lattice defects at the surface.