This study uses the Gini coefficient to examine the inequality in scholarly publishing for research institutions that have published articles in international journals in Korea for the past 20 years. The Gini coefficient was calculated using the number of papers and the cited-by counts, and the academic fields in which the Gini coefficient changed over time was identified. The result show that the inequality among Korean research institutions did not decrease compared to the 2000s, showing an inequality of g = 0.75-0.82. Broken down by academic fields, clinical medicine has the largest inequality, and the inequality in the art and humanities was found to have worsened in the past decade. This is the first study to understand the inequality in research output for all research institutions on country through the Gini coefficient. This study emphasizes on the use of Gini coefficients, to accurately measure the concentration of research output and its changes. By comparing differences among disciplines or countries, it can contribute to discussing the issue of inequality.