Abstract The oncogenic transcription factor TAL1 regulates the transcriptional program in T-ALL. ARID5B is one of the critical downstream targets of TAL1, which further activates the oncogenic regulatory circuit in T-ALL cells. Here, we elucidated the molecular functions of the noncoding RNA, ARID5B-inducing enhancer associated long noncoding RNA (ARIEL), in T-ALL pathogenesis. We demonstrated that ARIEL is specifically activated in TAL1+ T-ALL cases, and its expression is associated with ARID5B enhancer activity. ARIEL recruits mediator proteins to the ARID5B enhancer, promotes enhancer-promoter interactions, and activates the expression of ARID5B, thereby positively regulating the TAL1-induced transcriptional program and the MYC oncogene. The TAL1 complex coordinately regulates the expression of ARIEL. Knockdown of ARIEL inhibits cell growth and survival of T-ALL cells in culture and blocks disease progression in a murine xenograft model. Our results indicate that ARIEL plays an oncogenic role as an enhancer RNA in T-ALL.