BACKGROUND: Ambient temperature has a significant effect on the thyroid gland function. Thyroid gland can be assessed by ultrasonography and measurement of thyroid hormones. OBJECTIVES: The aim of this survey was normal ultrasonographic findings of thyroid gland in cat in warm (July) and cold (February) seasons. METHODS: The study was conducted on 30 native, adult healthy cats. Thyroid hormones including T3 and T4 were measured in each cat before ultrasonography. After finding thyroid gland, echogenesity, length, width and height of each lobe (right and left) were measured. RESULTS: Both thyroid lobes were scanable and symmetrical on each side. In sagittal plane it had a fusiform shape and in transverse plane it appeared as an oval or roughly triangular structure. The thyroid parenchyma was homogenously echogenic. The echogenecity of the gland was more than the neck muscles and no difference was seen between cold and warm seasons. Dimensions of each lobe were slightly larger in cold season than warm season. The differences in width and volume were significant (p<0.05) but the differences were not significant in length and height (p>0.05). The mean of the length, width, height and volume of both lobes were in normal range for cat with the same weight. Total means of length, width, height (mm) and volume (cm3) of both lobes were 17.2, 2.6, 2.7, and 0.07 in two seasons respectively. Also, the difference was significant in concentration of T3 and T4 hormones between cold and warm seasons, so that thyroid hormone concentrations were higher in cold season than warm season (p<0.05). CONCLUSIONS: It seems that the reduction in air temperature has an extraordinary effect on increasing thyroid gland size and thyroid hormone concentrations in native adult cats in Ahvaz district. This effect can be due to the influence of cold in the increase of body metabolism and thyroid gland function.