The aim of this study is to monitor paraquat-induced pulmonary fibrosis in rats with micro-computed tomography (micro-CT) findings. Adult rats were divided into four groups and given a single oral dosage of aqueous solution of paraquat at 0 mg/kg, 40 mg/kg, 60 mg/kg, and 80 mg/kg, respectively. In the control group, the color and luster of the lung samples appeared normal and no petechia was observed. In the experimental groups, some petechia was observed in lung samples, and fibroblast and fibrinogen were found in histological sections, and the ground-glass predominance and reticulation in micro-CT findings increased during the period from the 1st week to the 3rd week, and decreased in the 4th week after the administration. In the experimental groups, the lung weight of adult rats increased when the dosage of paraquat was increased, but the body weight increments of adult rats decreased, therefore the ratios of lung weight over body weight increased with increased dosage. From the analysis of 3D micro-CT images, the results show that the effective capacity volume of the lungs gradually decreased with increased dosage, therefore micro-CT is seen as a powerful tool for fast diagnosis and longitudinal monitoring of pulmonary fibrosis.