Variability in interlanguage has received growing attention in SLA. However, the variation and its sources in the interlanguage of L2 Chinese remain under-researched. This study investigated sources of inter-learner variation in the use of the ba construction (BC) by English and Korean speaking learners of L2 Chinese. A total of 110 adult learners were examined both in New Zealand and in China, with 22 native speakers of Chinese as control. A battery of three tasks (i.e., an oral production task prompted by video clips, an oral imitation task, and an untimed grammaticality judgement task conducted orally) was used to elicit two types of the ba construction (BC1 and BC2). The accuracy of the use of BC was examined in terms of two measures: oral scores (i.e., the average of the oral production and oral imitation scores) and metalinguistic scores (i.e., the average of the judgment and correction scores).The statistical analysis showed that the number of years of study, setting, first language, and starting age were the sources of the inter-learner variation. In addition, self-rated proficiency significantly correlated with both oral and metalinguistic scores of BC, whereas gender had no effect on the accurate use of BC. The findings are discussed in terms of the effects of these sources on oral and metalinguistic competencies. This study suggests that multiple sources account for the variation in BC, and that the effects of these sources differ somewhat in terms of the learners' oral and metalinguistic competencies.