Background: T-cell acute lymphoblastic leukemia (T-ALL) is considered a malignant tumor with a high mortality rate. To combat this disease, exploring the mechanism of T-ALL progression is urgently needed. Krüppel-like factors (KLFs) are known as the transcription factors and mediate series of biological processes. KLF9 is a member of the KLF family which could serve as a tumor suppressor gene in most solid tumors. GEO Database analysis showed that KLF9 expression in normal T cells was higher than T-ALL cell lines and patients. However, the possible role of KLF9 in T-ALL progression is still unclear.Objective: To uncover the possible effects of Krüppel-like transcription factor 9 (KLF9) on the progression of T-Acute lymphoblastic leukemia (T-ALL).Results: The expression of KLF9 was low in human T-ALL cells. KLF9 suppressed the viability of T-ALL cells. In addition, KLF9 stimulated the apoptosis as well as autophagy of T-ALL cells. Mechanically, KLF9 suppressed AKT/mTOR pathway in T-ALL cells.Conclusion: KLF9 suppressed viability and promoted autophagy as well as apoptosis in T-ALL cells by inhibiting AKT/mTOR pathway.