Exposure to the toxic herbicide paraquat (PQ) can lead to the active absorption and enrichment of alveolar epithelial cells, resulting in pulmonary fibrosis and respiratory failure. At present, no effective clinical treatment is available. Notably, however, patients infected with human acquired immunodeficiency virus (HIV) (with T lymphocyte deficiency) do not show pulmonary fibrosis after PQ poisoning, suggesting that T lymphocytes may be involved in the occurrence and pathological development of lung fibers following PQ exposure, although relevant studies remain limited. Here, we found that the degree of pulmonary fibrosis induced by intragastric administration of PQ in congenital immunodeficiency BALB/C (nu/nu) nude (T lymphocyte loss) mice was lower than that in normal mice. However, pulmonary fibrosis was aggravated after transplantation of BALB/C (nu/nu) T lymphocytes into congenital immunodeficiency mice. This study is the first to report on the involvement of T lymphocytes in the occurrence and pathological development of lung fibers induced by PQ exposure. Thus, T cells may be an important cellular target for the clinical treatment of pulmonary fibrosis caused by PQ.