Influenza A virus (IAV) undergoes RNA transcription by a unique capped mRNA-dependent transcription, which is carried out by the viral RNA-dependent RNA polymerase (RdRp), consisting of the viral PA, PB1 and PB2 proteins. But, how the viral RdRp utilizes cellular factors for viral transcription is not clear. Previously, we have conducted a genome-wide pooled shRNA screen to identify host factors important for influenza A virus replication. Ribosomal RNA processing 1 homolog B (RRP1B) was identified as one of the candidates. RRP1B is a nucleolar protein involved in ribosomal biogenesis. Upon IAV infection, part of RRP1B was translocated from the nucleolus to the nucleoplasm, where viral RNA synthesis likely takes place. The depletion of RRP1B significantly reduced IAV mRNA transcription in a mini-replicon assay and in virus-infected cells. Furthermore, we showed that RRP1B interacted with PB1 and PB2 of the RdRp and formed a coimmunoprecipitable complex with RdRp. The depletion of RRP1B reduced the amount of capped mRNA in the RdRp complex. Taken together, these findings indicate that RRP1B is a host factor essential for IAV transcription and provides a target for new antivirals.