Background: The E3 ligase SIAH1 is deregulated in human cancers and correlated with poor prognosis, but its contributions to chemoresistance in epithelial ovarian cancer (EOC) are not evident. Methods: SIAHI, RPS3, NF-κB (P65), FLAG and GFP protein levels were assessed by western blotting (WB) or immunohistochemistry (IHC). The mRNA levels were revealed by qRT-PCR. Colocalization of RPS3 and SIAH1 was detected by confocal microscopy and co-immunoprecipitation (CO-IP). RPS3 ubiquitination levels were detected by immunoprecipitation (IP). Cell functional experiments were performed and A2780 xenograft models were employed to expose the latent mechanisms of the SIAH1-RPS3-NF-κB axis as well as the role of SIAH1 in inhibiting chemoresistance in vitro and in vivo.Results: We show that SIAH1 is decreased in EOC tumour tissues and cell lines and negatively correlated with RPS3 level. SIAH1 overexpression suppresses tumour cell growth, colony formation, invasion, metastasis, and cisplatin resistance in vivo and in vitro. SIAH1 promoted RPS3 ubiquitination and degradation using the RING-finger domain, which was required for RPS3 localization to the cytoplasm for subsequent NF-κB inactivation, thereby conferring chemosensitivity. Moreover, ectopic expression of RPS3 or depletion of RPS3 ubiquitination mediated by SIAH1 via the K214R mutant significantly impaired cisplatin-induced tumour suppression in cells stably expressing SIAH1. Conclusions: Our findings reveal a tumour suppressor function of SIAH1 and provide evidence that the SIAH1-RPS3-NF-κB axis may act as an appealing strategy to tackle treatment resistance in EOC.