In agricultural fields, unregistered foreign workers who illegally reside in Korea with illegal work status takes a larger portion than registered foreign workers. This paper conducts quantitative and qualitative surveys and analyses on the scale of unregistered foreign workers in the agricultural sector and how they are employed. It presents the results and their implications on how to improve related policies and systems. Then, it suggests measures to improve the problem of unregistered foreign workers. First, it is necessary to establish a statistical basis for the agricultural labor force. Second, it is essential to identify the causes for the employment of unregistered foreign workers and improve the system accordingly. Third, there is a need to prepare a plan to move the organized and systemized supply channels of unregistered foreign workers to the institutional sphere.