This study aimed to investigate the impacts of extreme weather on the dry matter yield (DMY) of silage maize in South Korea. The maize data (n=3,041) were collected from various reports of the new variety of adaptability experiments by the Rural Development Administration (1978-2017). Eight weather variables were collected: mean temperature, low temperature, high temperature, maximum precipitation, accumulated precipitation, maximum wind speed, mean wind speed, and sunshine duration. These variables were calculated based on ten days within seeding to harvesting period. The box plot detected an outlier to distinguish extreme weather from normal weather. The difference in DMY between extreme and normal weather was determined using a t-test with a 5% significance level. As a result, outliers of high-extreme precipitation were observed in July and August. Low-extreme mean temperature was remarkable in middle May, middle June, and late July. Moreover, the difference in DMY between extreme and normal weather was greatest (5,597.76 kg/ha) during the maximum precipitation in early July. This indicates that the impact of heavy rainfall during the Korean monsoon season was fatal to the DMY of silage maize. However, in this study, the frequency of extreme weather was too low and should not be generalize. Thus, in the future, we plan to compare DMY with statistical simulations based on extreme distributions.