The purpose of this study was to describe the "The Effects of the Think Talk Write (TTW) Learning Model on the Students' Ability to Write Commercial Letters in Grade XI at SMA Negeri 1 V Koto Kampung Dalam". The research method used is an experiment. The research subjects were grade XI students of SMA Negeri 1 V Koto Kampung Dalam. The results of this study indicate that first, the ability to write a commercial letter using the think talk write learning model by grade XI Students of SMA Negeri 1 V Koto Kampung Dalam with an average value of 83.82 is included in the excellent category. Second, the ability to write a commercial letter by using a conventional learning model by grade XI students of SMA Negeri 1 V Koto Kampung Dalam with an average value of 67.29 included in the sufficient category. Third, Based on the results of the test results obtained tcount> ttable is 6.06> 1.66. So ho is rejected and ha is accepted. Thus it can be concluded that there is the influence effects of the Think Talk Write (TTW) learning model on the students' ability to write commercial letters in grade XI at SMA Negeri 1 V Koto Kampung Dalam.