Students in South East Asia often struggle with English /l/ and /r/. This study therefore set out to examine how Taiwanese pupils' perception of these sounds is influenced by cross-language effects. Most Taiwanese students have Mandarin as L1 and Taiwanese as L2 or vice versa, and English as L3. A same-different discrimination experiment was conducted to measure pupils' ability to discriminate between phonetically close English /r/ and /l/ and Mandarin /? / and /l/. The results show that L1-Mandarin pupils discriminate both the English consonant contrast and the Mandarin consonant contrast better than L1-Taiwanese pupils. Discrimination difficulty may be higher if two members of a contrast are perceived as belonging to a single L1 category.