Based on the dynamic and emerging nature of language aptitude, the paper reports an empirical study investigating the relationship between multilingual learning experiences and language aptitude through comparative analyses of language aptitude between second language (L2) and third language (L3) learners. Eighty-seven Chinese students who majored in English participated in this study. Among them, 41 participants were L2 English learners without additional foreign language learning experiences and 46 participants were L2 English learners with additional French or Japanese learning experiences. The findings showed that L3 learners outperformed L2 learners on the language aptitude measure and significant differences were found on explicit language analytical abilities. Furthermore, within-group analyses of the L3 learners found that L3 Japanese learners performed better on the vocabulary learning task and cross-linguistic similarities may help to interpret the finding. Further investigations of students' perceived language interaction indicated that students' perceptions of cross-linguistic interaction were consistent with the hypothesised interaction. Future research directions are also discussed in accordance with the current research findings.