摘要:Nowadays, learning English is very important because English is one of international languageswhich is usually used for communication by whole community. There are some parts of learningEnglish. One of the essential parts is grammar. Grammar is very necessary when we want to do awritten English. For example we can learn sentences, tenses, parts of speech, prepositions,clauses, and so on. The Problems identified in this research were: What is the mastery of thethird year students Gunadarma University in noun clauses? And What are the errors made by thethird year students Gunadarma University in noun clauses? The objectives of the study were: todescribe the mastery of the third year studentsgunadarma university in noun clauses, and to discuss what errors made by the third year studentsGunadarma University in noun clauses. The writer used the library research and the fieldresearch to complete the accomplishment of the scientific research paper. In the library research,the writer used some books which were related to the topic to help the writer in finding theoriesabout adjective clause. The writer also browsed theories from Internet to add theories besidefrom the books. In the field research, the writer used qualitative method by giving questionnairesrandomly to 36 populations in 3 SA 01, 3 SA 02, and 3 SA03 Faculty of Letters GunadarmaUniversity. Then the samples and all the population became samples of this research. Thesamples were then analyzed per number in each questionnaire and were concluded to the errorbased on the average score of total correct answers, and the percentages. After the data had beenanalyzed, the writer found that that the third year students of Faculty of Letters have understoodenough in understanding Noun Clauses with the percentage of error as much as 25,61 % or theyhad the ability as much as 74,39% (Letter grade C).