This study aimed at investigating whether or not integrated grammar teaching with writing improves the grammatical accuracy of students ’paragraph writing in grade 11. In addition, it tried to explore the students’ perception/attitude towards this instructional technique. There were totally 92 (47 experimental and 45 control group) students participated in this study. To do this, it employed quasi-experimental design. The data of this study were collected through testes (pre and post) and students’ questionnaire. Independent sample t-test and paired sample t-test were used to compute and analyze the pre-and post-test results. The questionnaire also analyzed quantitatively using frequency and percentage. Accordingly, the pretest result revealed that the experimental group and the control group had the same language performance in terms of grammatical accuracy in their writing quality before the treatment; whereas based on the posttest analysis result, the study group outperformed the control group. In addition, the result of paired sample t-test revealed that the experimental group improved their grammatical accuracy in posttest over pretest. Results of the students’ questionnaire also confirmed the results of the posttest. Generally, the null hypothesis that was there would not be any significant difference between the effectiveness of the methods of grammar instruction used in the study was rejected. Instead, the alternative hypothesis was drawn for conclusion in that teaching grammar integrated with writing was effective. On the basis of the findings of this study, it was concluded that integrated grammar teaching with writing could have a great value in improving students’ grammatical accuracy of their paragraph writing. Based on this, conclusions and recommendation and suggestions were made.