Iran, which is engaged and has a rich history and cultural, economic, politic ties with Turkey in the historical process, is one of the countries where Turkish is taught as a foreign language. In this country, while the history of the Turks and Turkish is ancient, the education of Turkish is a new situation. The mutual friendship and neighbourhood relations between Iran and Turkey enabled Turkish to become popular in this country. Because of the language relation between Turkish and Persian, the common cultural heritage, the interest and affinity they feel towards Turkey and Turkish, Iranians have been making a rapid progress while they have been learning Turkish as a foreign language. In spite of being successful especially in the fields of speaking and listening, they are faced with many problems when it comes to writing skill which is the basic area of activity in foreign language education. Writing is the last of basic language skills. The development of this skill should be put off for another time. The main reason for this is that the competence in speaking and comprehension in listening are understood as the indicators of foreign language knowledge. However, to speak a language and understand what you listen to are not enough to know a language. It is also required that a person can express himself/herself in writing in a foreign language. Despite the importance of writing in foreign language education, it can be said that the problems, which Iranian students are faced with while expressing themselves in writing, result from their ignorance of writing, lack of time in the in-class writing activities and also their ignorance of these activities by assigning them homework, the alphabet differences and the over-confidence that Iranians feel towards themselves. Nevertheless, high motivation and hard work is necessary for an effective writing in a foreign language. This study consists of the evaluation of the written expressions of 71 students, at B2 level in Tehran Yunus Emre Turkish Cultural Centre in 2012-2013 Spring Semester, according to Keshavarz’s (2011) error analysis with the aim of determining the errors which Iranians learning Turkish as a foreign language do in their written expressions and finding solutions to these errors. Research results concluded that Iranians who learn Turkish as a foreign language make spelling, punctuation, phonological, lexical, syntactic and process-based errors in their Turkish written expressions