Abstract： Objective To study the correlation of experimental acid inhalation and pulmonary fibrosis in rats and possible mechanism, and make a comparison with traditional bleomycin-induced fibrosis. Methods 120 healthy male SD rats were randomly divided into normal control group, bleomycin group,high-concentration hydrochloric acid group,middle-concentration hydrochloric acid group,and low-concentration hydrochloric acid group, 24 rats in each group. The rats in bleomycin group were intratracheally injected with bleomycin once to induce pulmonary fibrosis. The rats in hydrochloric acid groups were intratracheally dripped with different concentrations of hydrochloric acid once per week. The rats in normal control group were intratracheally dripped with saline once per week. Six rats of each group were randomly sacrificed on the 7th, 14th,28th and 42th day respectively. HE and Masson staining were used to evaluate the pathological changes of lung tissues. Reverse transcription-polymerase chain reaction was used to detect mRNA expression of transforming growth factor-β1. The expressions of type Ⅰ collagen and connective tissue growth factor were semi-quantitatively determinated by immunohistochemical method. Results The alveolitis level in hydrochloric acid groups was higher than that in normal control group (P<0. 01),reached a peak at two weeks,and then still maintained a relatively high status,reached or exceeded that in bleomycin group at the 28th day. The fibrosis level in hydrochloric acid groups gradually increased, was higher than that in normal control group (P<0. 05 or P <0. 01) ,but was not more than that in bleomycin group. The mRNA level of transforming growth factor-pi in lung tissues of hydrochloric acid group reached that in bleomycin group at the 28th day,and exceeded that in bleomycin group at the 42th day. The expression of type Ⅰ collagen in lung tissues of bleomycin group was higher than that in normal control group and hydrochloric acid groups at all time points (P<0. 05). The expression of connective tissue growth factor in high-and middle-concentration hydrochloric acid groups was higher than that in normal control group at the 14th day (P<0.05) .and increased with the infusion frequency and time. Conclusions This study reflects the correlation of acid inhalation caused by recurrent gastroesophageal acid reflux and pulmonary fibrosis, which provides the preliminary laboratory evidence for the relationship between the gastroesophageal reflux disease and idiopathic pulmonary fibrosis.