The use of machine translators (MTs) in teaching and learning English has increased in recent years. This study investigates how English-to-Korean and Korean-to-English MTs handle relative clause (RC) attachment. A total of 72 sentences 36 English and 36 Korean were collected from 16 research articles on RC attachment. The collected RC attachment items were categorized into three types: ambiguous, high attachment (HA), and low attachment (LA). English RCs with ambiguity (n=18) were translated into ambiguous Korean RCs; LA preference sentences (n=16) were translated into Korean RCs as LA. However, Korean RCs with ambiguity (n=34) were translated into ambiguous English RCs or HA preference sentences. Results showed that RCs with ambiguity in English and Korean were translated differently into the target language. The main cause of this distinction seemed to be that Korean RCs involving genitive case -uy were translated into English RCs using prepositions such as of and the genitive -’s. These two possible structures resulted in two different outcomes in English: (i) NP-of-NP structures, where ambiguity is preserved, or (ii) NP’s NP structures, where only HA preference was possible. These findings suggest that RC attachment is translated differently between the two languages by MTs.