Paraquat (PQ)-induced pulmonary toxicity is known to result in pulmonary edema, infiltration of inflammatory cells and damage to the alveolar epithelium, which may progress to severe fibrosis. Matrix metalloproteinases (MMPs) and their physiological inhibitors, tissue inhibitors of matrix metalloproteinases (TIMPs), which degrade and remodel the excess extracellular matrix, are believed to play an important role in the development of fibrotic tissue. In this study, we examined the sequential expression of MMP-2, MMP-9 and TIMP-1 in a rat model of pulmonary fibrosis induced by PQ. Adult male Sprague-Dawley rats were treated intraperitoneally with PQ (20 mg/kg) and saline (control group). Rats were sacrificed at days 1, 3, 7 and 21 after the PQ treatment. Lungs were excised for histological evaluation and immunohistochemical analyses, as well as the determination of collagen content, gene expression by fluorimeter-based quantitive RT-PCR assay and gelatinolytic activity by zymography. Lung MMP-2 and -9 mRNA expression progressively increased and reached a peak on day 7 after PQ treatment, while TIMP-1 mRNA levels in the PQ-treated lungs reached a peak on day 21 after modeling. Lung zymography revealed an increase in progelatinase B, progelatinase A and their active forms. In conclusion, unbalanced MMP/TIMP-1 expression and excessive gelatinolytic activity contribute to PQ-induced pulmonary fibrosis. Their precise role should be studied in depth as they may represent relevant therapeutic targets for PQ poisoning-induced pulmonary fibrosis.