Chemotherapy is the leading treatment for acute lymphoblastic leukemia (ALL). However, many ALL patients eventually develop relapses, the treatment of which remains a major challenge due to their chemoresistance phenotype. As a step towards this end, we here uncovered that relapsed ALL specimens exhibit a significantly lower expression of STAT6 but not of other STATs, when compared with their paired diagnosis specimens. Furthermore, STAT6 plays a distinctive role in chemosensitization of ALL cells to cytarabine (Ara-C), and T-box transcription factor 21 (TBX21) emerged as a plausible intrinsic biomarker of this Ara-C chemosensitization. We demonstrate that STAT6 undergoes SUMOylation on Lys-307 and sentrin/SUMO-specific protease 3 (SENP3)-mediated deSUMOylation in ALL cells. Most importantly, Ara-C specifically induced SENP3 expression and SENP3 knockdown sensitized ALL cells to Ara-C, with an impact equivalent to STAT6 knockout. These findings support the feedback resistance conferred upon ALL cells by Ara-C-induced SENP3 expression. Our findings uncover a novel role for STAT6 in ALL resistance to Ara-C and suggest that its targeted deprivation or pharmacological inhibition specifically sensitizes ALL cells to Ara-C, offering a plausible modality to surmount Ara-C resistance in future ALL treatment.