This study aims to investigate substitution error in using embedded sentences of Korean language learners. For this purpose, learners` about 7,000 sentences were collected to analyze and categorized into two types: 1) substitution between items of different embedded clauses, 2) substitution between items of similar but different ones in the same embedded clause. The first type of error such as using adnominal clause instead of nominal clause or using quotative clause instead of adnominal clause shows the need for teaching sentence structure and macro grammar in parallel with teaching individual grammar items. The second type of error happens when learners are ignorant of syntactic restriction of each items. From the result of this study it became clear what kind of the syntactic restriction is to be specified in educational grammar for learners.