This current study aimed at creating a 3D virtual environment on Second Life particularly for special education students to enhance their first language, Mandarin, learning in vocabulary and sentence structures. Four students aged between 8 and 9 participated in this research. In addition to their inherent disabilities (mild autism spectrum disorder, attention-deficit hyperactivity disorder, or mild mental retardation), all the four participants suffer from delayed language development. The purpose of the 3- month study was therefore to establish a platform enhancing their learning of Mandarin Chinese. A design-based qualitative design was adopted in this study. The collected data included in-class observation, video clips of learning process, and post-study interviews with the four disabled children. Additionally, parents' comments on their children's oral expression skills at home were also collected. Through a two-cycle investigation, this research proposed six categories of Human-computer interface (HCI) design principles for using virtual worlds to enhance special education students' Mandarin learning. In addition, both the interview results and the parents' comments confirmed the effects of using this platform for special education students' learning.