Abstract: Objective To explore the expression level of inhibitor of DNA binding 4(ID4) in T-cell acute lymphoblastic leukemia(T-ALL), and to determine the correlation and mechanism between NOTCH1 and ID4. Methods The expression levels of ID4 in T-ALL patients and normal donors, as well as the correlation of NOTCH1 and ID4, were analyzed from the databases of Oncomine and Pieters R. ID4 mRNA and protein levels were detected by qRT-PCR and Western blot after NOTCH1 inhibition or activation, which were adopted to verify the correlation. MicroRNA-342 (miR-342) was predicted to target ID4 with the approach of bioinformatics, and the dual luciferase reporter system was carried out to verify the prediction. ID4 mRNA and protein levels were detected by qRT-PCR after overexpressing or silencing miR-342. MiR-342 expression level was detected by qRT-PCR and Western blot after NOTCH1 inhibition or activation. Results ID4 expression level in T-ALL patients was significantly lower than that in normal donors(P＜0.01); ID4 was negatively regulated by NOTCH1(P＜0.05); The dual luciferase reporter system validated ID4 as a specific target gene of miR-342; Down-regulation of miR-342 resulted in sharp increase of ID4 mRNA and protein (P＜0.05), and upregulation of miR-342 resulted in sharp decrease of ID4 mRNA and protein (P＜0.05); NOTCH1 inhibition could down-regulate the expression of miR-342, and NOTCH1 activation could up-regulate the expression of miR-342. Conclusion NOTCH1 activates the negatively regulatory role of miR-342 for ID4, then downregulates tumor suppressor gene ID4 expression, and may contribute to the pathogenesis of T-ALL.