Although writing has been considered as the most difficult of the four English skills as mentioned in Introduction, it is feasible for L2 student writers to enhance their writing accuracy. As a rule, compared to a medical service, prior to coming up with an appropriate remedy, a disease should be first diagnosed its characteristics of symptoms. Similar to the nature of this study, before a good piece of writing with as few errors as possible is produced, the causes of ineffective writing should also be identified. According to the results of this study, it can be firmly said that L1 interference categories of each writing genre varied in terms of L1 syntactic and semantic properties. That is, in narration, the L1 interference categories with frequency counts of more than 100 errors were verb tense (382, 26.98%), word choice (178, 12.57%), sentence structure (150, 10.59%)