Since English is the Second Language (L2 ) that English-majored students at Can Tho University (CTU), the Mekong Delta Region, Vietnam, have to learn, writing seems to be the most difficult area in the four skills for the English language learners. The present study focuses on common mistakes in writing paragraphs of the first-year students majoring in English at Can Tho University¬, in the academic year 2013-2014. The relevant data for the study was collected from the students’ written products and the in-depth interviews. The students were asked to write a free paragraph about “Your new life in Can Tho University” in English. The time allowed to do the test was 30 minutes. Each of the students made a paragraph of at least 1 20 words. The total number of papers to be analyzed was 60, and all of the mistakes in the paragraphs were identified and classified into thirteen categories. The results reported that the number of the “Word Formation”, and “Word Choice” mistakes in participants’ writing were the most serious or frequent, whilst the least commonly made mistakes were “ Subject/ Verb Agreement” , and “ Word Order” . The interviews analysis also revealed that there were apparent connections between analyzed data from participants’ papers and teachers’ responses as well as students in the interviews. From these results, some implications are suggested to help students reduce grammatical mistakes in their papers as well as help English teachers who will give positive influence to their students’ needs