In this review, we report real time imaging of abomasal curd formation in preruminant calves by ultrasonography. Ultrasonographic images of the abomasum and simultaneously obtained cross-sectional topographic images showed that the curd was visualised as an echogenic image with a clear outline and whey as an anechoic image. The time course ultrasonographic evaluation of curd formation indicated that the appropriate time for evaluating curd formation is between 1 and 2 h after feeding milk replacer, when a large curd could be imaged in calves fed clotting milk replacer. Ultrasonographic evaluation of curd formation in 29 preruminant calves that were fed a clotting milk replacer provided a new finding that the abomasal curd formation was absent in 8 of the 29 calves. Thus we propose that the ultrasonographic method for evaluating abomasal curd formation provides direct evidence of curd formation. It is a practical and non-invasive technique of distinguishing curd-forming and non-curd-forming calves, which would be useful in investigating the physiological function of curd formation in preruminant calves.