The present study was focused on acquisition of Chinese relative clauses (RCs) by second language (L2) learners and whether this acquisition was influenced by RC linguistic features, learners' Chinese proficiency levels, and their first language (L1). Data were gathered via a Chinese reading comprehension test, a grammaticality judgment task, a sentence combination task, a sentence formation task, and post-task interviews. An analysis of 46 Chinese learners' and 22 native speakers' performances on these tasks and 15 learners' perspectives from the interviews revealed that the acquisition of RCs was challenging for learners, particularly with the use of the RC marker de. Furthermore, the types of RC and Chinese proficiency levels significantly impacted the learners' acquisition of RCs. The results indicated that learners could comprehend both subject RCs (SRCs) and object RCs (ORCs) with comparable accuracy, but they produced more correct sentences with ORCs than with SRCs. Additionally, learners' L1 influenced their acquisition of Chinese RCs, which was evident from the errors made with de as an RC marker and the production of Chinese RCs with English word order. The interview data confirmed that learners' perceptions of Chinese RCs played a role in the L1 transfer effect on their acquisition. The results of the current study have implications for teaching Chinese RCs and suggest the need for frequent input on RCs in classroom instruction. Task-based language teaching activities and multimodal input can provide more meaningful and engaging input to learners and improve their accuracy and fluency in using RCs. Explicit instruction to explain the syntactic features of RCs to learners is also recommended. RC instruction should start with SRC and then proceed to ORC. Teachers are encouraged to communicate with students about their perceptions of the differences and similarities between RCs in their L1 and the target language to further analyze their errors and learning strategies. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]