The Jun activation-domain binding protein 1 (Jab1) induces p53 nuclear export and cytoplasmic degradation. However, the underlying mechanism is not clearly addressed. Here, we identify that phosphorylation at threonine 155 residue is indispensable for Jab1-mediated p53 nuclear export. Jab1 stimulated phosphorylation of p53 at T155, which was inhibited by curcumin, an inhibitor of COP9 signalosome (CSN)-associated kinases. T155E mutant, which mimics phosphorylated p53, exhibited spontaneous cytoplasmic localization in the absence of Jab1. This process was prevented by leptinomycin B (LMB), but not by curcumin. The substitution of threonine 155 to valine (T155V) restrained Jab1-mediated p53 nuclear export, indicating that phosphorylation at this site is essential for Jab1-mediated regulation of p53. Although T155E can be localized in the cytoplasm in the absence of Mdm2, the translocation of T155E was significantly enhanced by ectopic Hdm2 expression. Our data suggest that Jab1-mediated phosphorylation of p53 at Thr155 residue mediates nuclear export of p53.