Committing errors and feedback in writing are important in the process of language acquisition (Corder, 1975; Foster et al., 1988; Krashen, 1981; Marina et al., 2005; Salehi et al., 2018; Valizadeh et al., 2020). In Vietnam, however, error-analysis in writing in the contexts of EFL students has not been investigated fully. This research study explores and examines common mistakes of second-year English language students in writing English. The research was conducted with different tools including error assessment of some writing assignments, a survey to measure the ability to recognize errors in English writing, and interviews with some participants from an insider's perspective. The results found that the level for each of the written errors in the results varied widely. Certain types of errors were correctly identified by research participants and their ability to correct the issues was demonstrated properly at some points. However, most of them were unable to recognize errors, suggesting inconsistency in the ability to recognize and correct errors. Specifically, the research found a list of types of errors which occur while writing English from the phrase level to the sentence level, among other groups of errors while writing. This study could foster a trend to develop strategies to help students learn English better from both teachers' and students' point of view in today's English training programs.