In order to investigate the effect of curcumin combined with all-trans retinoid acid (ATRA) on differentiation of ATRA-resistant acute promyelocytic leukemia (APL) cells and its molecular mechanism, the NB4-R1, an ATRA-resistant APL cells, was used as a model, counting of NB4-R1 and cell morphologic observation were performed, the effect of curcumin alone or combined with ATRA on proliferation, differentiation of NB4-R1 cells was detected by flow cytometry (FCM), the change of AKT phosphorylation in cell differentiation was detected by Western blot. The results showed that ATRA had no influence on NB4-R1 cell proliferation, but enhanced the inhibitory effect of curcumin on NB4-R1 cell growth; the curcumin or ATRA alone did not affect NB4-R1 differentiation; curcumin combined with ATRA could obviously induce CD11b expression; the cell morphology showed obvious differentiation characteristics. ATRA could promote phosphorylation of AKT in NB4 cells at short time, but not had effect on phosphorylation of AKT in NB4-R1 cells; the curcumin could enhance the phosphorylation of AKT in NB4-1R cells, the curcumin combined with ATRA could further enhance the phosphorylation of AKT. It is concluded that PI3K/AKT pathway inactivation may be one of the factors of drug resistance in APL and curcumin promotes differentiation of NB4-R1 through activating PI3K/AKT pathway.