This study aims to do a comparative analysis of the writing errors of Turkish, Azerbaijani and Syrian university students studying in English preparatory classes in the context of grammatical, lexical and spelling errors. The data of this qualitative case study were obtained from the 15 English preparatory class students from Turkey (N=5), Syria (N=5) and Azerbaijan (N=5). They were studying at A2 (pre-intermediate) level classes at the school of foreign languages of a state university in the northwest of Turkey. In order to get the information from the writing errors made by the students, 60 pieces of their writing portfolio papers were collected through the document analysis technique. The research data were analyzed through the content analysis. The results revealed that Turkish, Azerbaijani and Syrian students have some differences in terms of both the number and the types of writing errors. On the other hand, Turkish and Azerbaijani students also have a great number of similarities, but they differ from Syrian students in almost all types of errors. In the light of the results of the study, it has been concluded that most of the errors resulted from the mother tongue and culture-related negative transfers are frequently encountered ones in the teaching process of writing skills.