Morphological traits of the whole udder (circumference, width, height, and length), teats (angle, length and width), udder cistern (teat opening and cistern height), and milk yield were measured over one lactation in a total of 18 ewes (nine Chilota and nine Suffolk Down sheep) belonging to the same experimental flock (Centro Experimental INIA Butalcura, Chiloé, Chile). Analysis of variance showed significant effects for breed, sheep within breed, and stage of lactation. Chilota ewes evidenced greater udder circumference (433 mm), udder length (86 mm), teat opening (96°), and milk yield (947 mL d-1) than Suffolk Down ewes (410 mm, 77 mm, 93°, and 559 mL d-1, respectively). Udder circumference, udder width, udder length, cistern height and teat size significantly decreased throughout lactation. Repeatabilities of all traits were between 0.17 and 0.60; the highest repeatability was for udder circumference. This trait is easy to measure and had a discriminatory value for breed differentiation. In conclusion, Chilota sheep had a dairy aptitude greater than Suffolk Down sheep and similar to Spanish and Mediterranean dairy sheep breeds at beginning of their breeding programs.