The current study aimed to know the effect of pyridine on the histological structure of the lungs in rabbits. The study included 15 rabbits, with different ages ranging between 9-6 months and with different weights from (1.100-1.653) kg. The animals were divided into three groups, and each group contained 5 rabbits. The animals were placed independently and were as follows: the first group was the control group, and the second and third group were the experimental groups and included 5 rabbits for each group. Animals were injected with pyridine under the gel at a concentration of (100,200) μl of pyridine/kg of body weight for 30 days at one concentration for each group. After completing the experiment, the animals were sacrificed, dissected and extracted from the lungs, and their tissue sections were prepared. The results of the current study showed clear changes in the weights of rabbits treated with pyridine, as the weights of all experimental group animals decreased, and this decrease was affected by the increase in concentration, reaching a bear (0.850-1.400) kg. The current study of all animals treated with pyridine showed clear histological changes to the histological structure of the lungs, which included the occurrence of necrosis and separation of cells of the epithelial layer lining the bronchioles, the emergence of pulmonary oedema, macrophages, active transport vesicles, congestion and haemorrhage, and there was also an enlargement of the muscle layer, infiltration and cellular accumulation in the affected places. Severe congestion of the alveoli and rupture of the alveolar septa, as well as a change in the thickness of the alveolar septa, which led to a change in the diameters of the alveoli and an expansion in the tissue points according to the increase in concentration. The alveolar diameters in the experimental groups reached (22.8- 27.6) micrometres, respectively, compared to the control group, where its diameter was (13.6) micrometre.