Error analysis researches have a significant role in the realm of English teaching programs, especially in EFL contexts. They can be in use by teachers, learners, textbook providers, education system and so on. This study investigates the Iranian EFL linguistics taxonomy of morpho-syntactic errors and error analysis. Participants of this study are nine pre-intermediate instructed Persian learners of English, all of them are female with the average age of fifteen studying in an English institute in Rasht, Iran. They are asked to write an essay on the title of “What do you want to do in future?". After collecting the data and categorizing and identifying the erroneous areas in their written work, they are analyzed by the aid of the linguistic taxonomy of errors. The results of this study showed that "use of prepositions" is the most frequent part of their errors and after that the "use of articles". It is noticeable that the minimum frequency is related to errors in the "use of relative clauses" and "relative pronouns" and "wrong use of verbs".