The transcription factor p53 and AP-1 play an important role in cellular proliferation, transformation and death. In this study, we investigated the role of a novel human gene, TTC5 (tetratricopeptide repeat domain 5), in the regulation of cell signaling pathway and cell viability. TTC5 is a member of the TTC family of proteins and has previously been shown to participate in cellular stress response. Here we demonstrate for the first time that TTC5 significantly activates p53 pathway and inhibits AP-1 transcriptional activity. Further investigation revealed that overexpression of TTC5 up-regulated p53 and p21 expression, and significantly inhibited transcriptional activity, expression and phosphorylation of c-Jun. As for the upstream of signaling pathway of AP-1, our study demonstrated that overexpression of TTC5 significantly down-regulated the expression and phosphorylation of JNK/SAPK. Moreover, overexpression of TTC5 repressed cell proliferation and induced S phase cell cycle arrest. These results indicated that TTC5 may regulate cell viability by p53 and AP-1 signaling pathway.