ABSTRAK This study explores the acquisition of obligatory grammatical elements, those are verb-ing, plural, articles, and subject-verb agreement. The subjects are 63 students of English Department taking essay writing course. The technique that is used is obligatory occasion analysis. The result shows that the highest rank in the order scored is 100% and the lowest rank is 47,8%. It shows that every grammatical elements has different acquisiton orders on it is sub items. The conclution is subject are able to use grammatical features that the topic are recognized. It needs verification from future researchers. The instrument that is used in this study is open-ended. It means it is possible for subjects to avoid grammatical elements that they do not master
