This study aimed to investigate Korean grammatical difficulty based on the accuracy rate of grammaticality judgment test (hereafter, GJT). To meet the goal, the study employed listening typed GJT with 314 items of 19 Korean grammatical features. The study conducted the test to 131 intermediate level learners of Korean from China, France, Japan, and the US. The most difficult features with low accuracy rate were retrospective prefinal ending ``-de-`` for American and French learners, auxiliary particle ``un/nun`` for Chinese learners, and conjunctive ending ``-nerago`` for Japanese learners. On the contrary, the least difficult features were honorific for Chinese, French, ad Japanese learners, and negation for American learners, Each subcategory of classifiers, numerals and conjugations showed very different accuracy rate following to their availability and frequency. Although classifiers ``pul``, ``keru``, and ``chae`` showed very low accuracy rate, classifier ``mari`` and ``kae`` and numeral for age ``-sal`` showed very high accuracy rate.