It is known that blood flow through the carotid artery is decreased during pregnancy, which may be due to a pregnancy-associated increase in the sensitivity of this artery to vasoconstrictors. Recent studies have shown that alteration of blood flow or pressure could remodel some arteries over a short time frame. However, the possibility of remodelling of the carotid artery during pregnancy has not yet been examined. Therefore, the aim of the present study was to study the morphometrical and stereological characteristics of guinea-pig carotid artery during different stages of pregnancy (non-pregnant, early-pregnant, mid-pregnant, late-pregnant, n = 8-10 for each group). The cross-sectional area of the different layers of the carotid artery and the cross-sectional area of endothelial and smooth muscle cells were measured using both light and electron microscopy. The values of internal diameter and cross-sectional area of adventitia were not significantly different, regardless of the pregnancy status. In contrast, external diameter, wall thickness and cross-sectional areas of media and intima progressively and significantly decreased during pregnancy. In addition, volume/surface density ratio of intima and media also significantly and progressively decreased during pregnancy, suggesting hypotrophy of endothelial and smooth muscle cells of carotid artery. Indeed, electron microscopy revealed that the size, defined as cross-sectional area, of endothelial and smooth muscle cells was significantly decreased during different stages of pregnancy. It is concluded that during pregnancy there is thinning of the intimal and medial layers of guinea-pig carotid artery, which reflect pregnancy-associated hypotrophy of carotid artery endothelial and smooth muscle cells.