N(pro) is a multifunctional autoprotease unique to pestiviruses. The interacting partners of the N(pro) protein of classical swine fever virus (CSFV), a swine pestivirus, have been insufficiently defined. Using a yeast two-hybrid screen, we identified poly(C)-binding protein 1 (PCBP1) as a novel interacting partner of the CSFV N(pro) protein and confirmed this by coimmunoprecipitation, glutathione S-transferase (GST) pulldown, and confocal assays. Knockdown of PCBP1 by small interfering RNA suppressed CSFV growth, while overexpression of PCBP1 promoted CSFV growth. Furthermore, we showed that type I interferon was downregulated by PCBP1, as well as N(pro). Our results suggest that cellular PCBP1 positively modulates CSFV growth.