Research has shown that writing skill of Iranian learners is not at a satisfactory level. One of the ways to develop writing ability is improving strategic behavior of learners. The current study set out to compare writing performances and patterns of using metacognitive strategies in bilinguals and monolinguals as well as senior and freshmen students. A total of 176 English major university students took part in the study (88 bilinguals and 88 monolinguals). Data were collected through three instruments: a background questionnaire, a writing metacognitive strategy questionnaire, and participants’ compositions. A two-way factorial ANOVA was used to analyze the data obtained through the strategy questionnaire. Since the composition data were not parametric two Kruskall-Wallis tests were employed for data analysis. The results revealed that bilinguals used more metacognitive strategies and had higher writing scores than monolinguals. In addition, seniors had better writing performance than freshmen while the difference between them in using strategies was not significant. Based on the results it can be concluded that teaching writing metacognitive strategies may result in better writing performance.