The purpose of the current study is to investigate the affixation process of the Korean noun derivational suffix, ‘-러’ [lʌ], which means ‘a person who does something1.’ This suffix is assumed to be originate from the English suffix ‘-er’ [ər] and it is booming in Korean vocabulary recently as in ‘불참러’ [pultʃamlʌ] ‘a person who does not attend.’ However, unlike the English noun derivational suffixation ‘-er,’ the Korean allomorphic form [lʌ] shows somewhat intriguing suffixation patterns. This contemporary Korean derivational suffix shows very productive and formative affixation behaviors onto bases. In the present study, the Korean allomorphic data of [lʌ] suffixation will be provided. In the data, the structures of the bases will also be discussed. That is, we will examine whether the base consists of a single morpheme or more than two morphemes (or parts of those morphemes). We also provide a possible lexical morphological rule for the suffix [lʌ]. In the current paper, Optimality Theoretic (OT, Prince and Smolensky 1993, McCarthy and Prince 1995) analyses will also be presented. (Dong-A University)