Abstract-Nowadays, having a good mastery in writing skills plays a pivotal role in achieving success. Hence, it seems that further improvement in teaching writing in general, and providing corrective feedback on students' errors in particular, might be necessary. There is no doubt that teacher written feedback plays an essential role in English writing classes. However, in spite of tremendous contribution of time and attempt from teachers and students, the feedback provision process is yet far away from ideal. Thus, a search for potential ways to improve the effectiveness of providing corrective feedback makes the motivation for this research study. The current study aimed at exploring the impact of Collaborative Negotiated Feedback on Iranian intermediate EFL learners' writing and compared it with Teacher-written feedback. The study involved two groups of Iranian Intermediate EFL learners (30 students in each), consisting male and female, aged from 19 to 25, who were chosen through convenience sampling. In both groups, the same materials regarding different kinds of essay and paragraph organization were covered and implemented. While experimental group was provided with collaborative negotiated feedback, the control group was provided with the teacher's written feedback during the sessions. After Carrying out the treatment, the mean scores of the extracted data from pre-test/post-test of both groups were compared using independent sample t-test. The present researcher came to this conclusion that participants of the experimental group, who were exposed to collaborative negotiated feedback, outperformed the other group. The triangulation of three different sources; Pre/Post-test comparison, the questionnaire and interviews provide evidences in support of the efficacy of Collaborative Negotiated Feedback.