The study was conducted to analyze and assess the students’ writing performance in the written composition in term of analyzing their frequent grammatical errors along morphology, lexicon, syntax, and mechanics that they often make and to find out the main causes that affect students’ written errors, it is believed that students’ writing competence will be improved.

The quantitative research method was used in the study, which involved Ferris (2003) Analysis Model for Common ESL Writing Errors for identification and classification of errors. The survey investigated 67 freshmen at Thai Nguyen University of Medicine and Pharmacy. Besides, personal observation and interviews were applied to collect more data for the analysis. Based on the results of the analysis and discussion, the researcher has proposed a supplementary writing syllabus to improve their writing performance.