The merger of the Mandarin [s]~[ù] contrast, known as “deretroflexion”, frequently occurs in Mandarin spoken by bilingual Southern Min speakers, whose L1 lacks the retroflex category. This study explores the production of the Mandarin alveolar-retroflex contrast by bilingual speakers of Quanzhou Southern Min (L1) and Mandarin (L2) in two different vowel contexts ([a] vs. [u]). Our bilingual speakers’ contrast production was evaluated using a perceptual identification task by L1 Mandarin speakers, showing only a small subset of our sample who maintained the [s]~[ù] contrast. We found significant Center of Gravity (CoG) differences between the two target fricatives for “distinctive” speakers, with this difference being larger in the context of [a] than [u]. For all speakers, the acoustic difference between the target fricatives increased with increased exposure to and use of Mandarin.