The study was aimed to see how teacher‟s weblog could be utilized to encourage collaborative learning in a portfolio assessment of a foreign/second language writing. A model of teacher‟s weblog with a Facebook login was designed. Students collect their first draft of writing text by publishing it on the weblog, then their peers read and provide feedbacks for improvement of the second draft. Twenty six students of English Teacher Education Department of Sultan Agung Islamic University Semarang Central Java taking the course of Writing 3 participated as the subjects of the study. Data collected by questionnaire show that they were happy to have their works published on the weblog. Since the writings would possibly be read by many people, they would prepare the writing assignment better. They also admitted that they could learn from the writing posts of their peers. From 5 categories of peer feedbacks (organization, content, grammar, style, and mechanics), grammar feedback in which students identify the errors or mistakes in grammar and provide suggestions for improvement, is the most frequent feedbacks offered by students (48.8%), followed by style (15.6%), mechanics (14.1%), organization (12.5%), and content (9.4%). This practical model of portfolio not only eases the teacher but also encourages the students to learn collaboratively. Students can help each other improve the quality of their writing by receiving or providing feedbacks for their peers.