The main feature in the cow ownership in the Koryo Dynasty is that the peasantry was losing their ownership of cows. The cow ownership in the Koryo Dynasty was transferred from general peasants to bureaucrats and merchants. We can find internal and external causes for this. Among internal causes is that it was very costly to raise cows, which is thought to block general peasants from using them in their agricultural practices. The frequent droughts in the Dynasty caused the shortage of funds for growing cows and forced farmers to sell their agricultural equipment for food. As a result, cows became monopolized by bureaucrats and merchants. In the end of the Koryo Dynasty, ownership of cows by merchants and foreigners gave rise a serious problem, reducing the opportunities of peasants' using cows in their agricultural practices. Therefore it can be assumed that the decrease of productivity accelerated the loss of cow ownership of peasants. The second cause in the ownership change is for the government to start granting lands with the rights to develop them. The right was called 'Sa Pae(陽牌)'. In order to develop those uncultivated lands, massive workforces were needed. However, King ChungRyul(忠烈王) granted 'Sa Pae'to the class which has insufficient workforces for developing the lands. The only choice of the land owners could afford was to deprive farmers of cows to secure enough workforces. The final cause is external. The Won Dynasty in China Mass-purchasing Korean cows generated the changes in the cow ownership. In particular, after abolishing garrison farm, the cows used for garrison farm were sold to foreign countries by merchants or bureaucrats, not used by peasants, which ultimately limited the ownership of plowing cows by peasants. These causes of the cow ownership changes increased the ownership of arable lands and agriculture equipment by the privileged. In this situation, peasants had no choice but to work for the landowners, not owning their own lands. The changes of agriculture means caused the monopoly of agricultural productivity by the privileged, which in the end of the Dynasty created farms where farmers could not have their own lands.