Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive interstitial lung disease with unknown etiology and undefined treatment modality. Fibroblasts are regarded as the major cell type that mediates the onset and progression of lung fibrosis by secreting large amounts of extracellular matrix (ECM) proteins, such as connective tissue growth factor (CTGF/CCN2). Current knowledge confers a crucial role of CCN2 in lung fibrosis. CCN5, another member of the CCN family, has been suggested to play an inhibitory role in some fibrotic diseases, such as cardiac fibrosis. However, the role of CCN5 in the process of IPF remains unknown. In the present study, using western blot analysis, we demonstrate that CCN2 is highly expressed in fibroblasts derived from IPF tissue, but is only slightly expressed in normal human lung fibroblasts. However, CCN5 was weakly expressed in all the above cells. qRT-PCR revealed that transforming growth factor (TGF)-β1 stimulation increased CCN2 expression in the IPF-derived cultures of primary human lung fibroblasts (PIFs) in a time- and concentration-dependent manner, but only slightly affected the expression of CCN5. The overexpression of CCN5 induced by the transfection of PIFs with recombinant plasmid did not affect cell viability, proliferation and apoptosis; however, it significantly suppressed the expression of CCN2, α-smooth muscle actin (α-SMA) and collagen type I. The TGF-β1-induced upregulation of the phosphorylation of Akt was reversed by CCN5 overexpression. Our results also demonstrated that adenovirus-mediated CCN5 overexpression in a mouse model of bleomycin-induced IPF significantly decreased the hydroxyproline content in the lungs, as well as TGF-β1 expression in bronchoalveolar lavage fluid. Taken together, our data demonstrate that CCN5 exerts an inhibitory effect on the fibrotic phenotypes of pulmonary fibroblasts in vitro and in vivo, and as such may be a promising target for the treatment of IPF.