This study investigated the postpartum (PP) uterine involution in nine multiparous Martina Franca jennies with at term, normal, and singleton foaling. Transrectal ultrasonography performed at Days 1, 3, 7, 14, 21, and 28 showed that the uterine tip diameters did not differ between the post-pregnant (PPH) and non-post-pregnant uterine horns (NPPH), whereas the diameter of the middle PPH was larger than the NPPH until Day 7 (p < 0.05). The diameter of the corpora-cornual junction resulted larger in the PPH than NPPH at Day 7 (p < 0.05). At Day 3, the microcaruncolae were not detected. Endometrial glands (GL) number increased, with the highest value on Day 28. Endometrial GL area and perimeter decreased (p < 0.001) from Day 1 to Day 28. Epithelial thickness increased from Days 1-3 to Day 7 (p < 0.001), and concurrently with the foal heat to Day 14 (p < 0.001), with a decrease at Days 21-28. A marked neutrophils reduction on Day 7 and eosinophil increase from the first three days to Days 7-14 was observed. The results suggest that, in Martina Franca jennies with normal foaling, the PP uterine involution can be considered complete on Day 14.