Abstract-This study was an attempt to examine the effect of L2 writing ability on L1 writing ability from a multilingual perspective. To this end, 120 students of Isfahan University, half English majors and half nonEnglish majors, were assigned to 4 groups, consisting of 30 English major senior students, 30 English major freshman students, 30 non-English major senior students and 30 non-English major freshman students (Accounting and Management majors). All the participants were asked to write a paragraph of about 150 words on the topic "What are your plans for the future?" in Farsi. For analyzing the possible syntactic development in each participant's writing ability, 2 measuring criteria were used: 1) Loban Index, and 2) Tunit. To summarize and analyze the data, both descriptive and inferential statistics were utilized. A one-way ANOVA was run to compare the means of the 4 groups on the Loban Index criterion to see whether their differences were statistically significant. In order to observe the real differences of the means of the 4 groups based on the T-unit criterion and also to specify the interaction between the levels of the independent variables, a one-way ANOVA was run. The results of the 4 groups who studied the L2 (i.e., English) with different intensity indicated that the English major senior students outperformed the other 3 groups in the obtained Fvalue on the Loban Index criterion. The findings support the idea that intensive and successful L2 learning can have a beneficial influence on the development of L1 writing ability.