Objectives/Hypothesis: Dysregulation of microRNAs (miRNAs) has recently been shown in chronic rhinosinusitis (CRS), the biogenesis and function of which are modulated by miRNA machinery proteins. The expression of these proteins in inflammatory airway diseases is unclear. The aim of this study was to investigate the expression of miRNA machinery components in CRS. Study Design: Casecontrol experimental study. Methods: The mRNA expression levels of miRNA machinery components including Drosha, Dicer, protein activator of the interferon-induced protein kinase (PACT), human immunodeficiency virus transactivating response RNA-binding protein, fragile X mental retardation protein, and argonaute 2/eukaryotic translation initiation factor 2C, 2 in nasal biopsies from control, CRS without nasal polyps (CRSsNP), eosinophilic, and noneosinophilic CRS with nasal polyps (CRSwNP) subjects were determined by quantitative reverse transcription polymerase chain reaction. Immunohistochemical staining was employed to examine the protein expression of PACT and the cellular source of PACT. Results: Among the tested components, only PACT mRNA expression was found to be altered in CRS, the levels of which were upregulated in CRSwNP as compared with control. In comparison with control and CRSsNP, PACT protein expression was also significantly upregulated in CRSwNP, with a further increase in eosinophilic CRSwNP. PACT was mainly expressed in CD138+ plasma cells. A higher percentage of PACT-positive plasma cells in total plasma cells was detected in eosinophilic CRSwNP than in noneosinophilic CRSwNP. PACT protein expression correlated with disease severity and eosinophil infiltration. Conclusions: PACT may be associated with the plasma cell function and eosinophilic inflammation in CRSwNP. However, further experimentation is needed to clarify the functions of PACT.