This study aimed to analyze common syntactic errors found in the argumentative essays of third-year English major students at the Faculty of Foreign Languages, Van Lang University, Vietnam. Quantitative and qualitative methods were used to obtain data in this study. The quantitative approach involved counting and calculating the frequency, percentage, and ranking of syntactic errors, while the qualitative method was adopted to explain these errors. The instrument for collecting data was argumentative essays written by 37 third-year English majors enrolling in Writing-5 at Van Lang University. Microsoft Word was used to collect and analyze syntactic errors and sentence structures, while Microsoft Excel was employed to calculate the frequency and rank of these errors and structures. The results found that the five most frequent errors in their essays were at the noun phrase and sentence levels. These errors included run-on sentences, preposition errors, article errors, sentence fragments, and pronoun errors. Through error analysis, it was indicated that the majority of errors made by students were due to the negative transfer from their first language and the literal translation. Based on the findings, language teachers and syllabus designers could use these results as guidance to design appropriate teaching methods and materials.