This research aims to determine the influence of Think Talk Write (TTW) strategy to understand of mathematical concept students class VIII SMP Negeri 2 Lubuklinggau. The method used in this research is pure experiment. The population is the entire class VIII SMP Negeri 2 Lubuklinggau academic year 2016/2017 which amounts to 444 students, as the sample is class VIII.9 as experimental class and class VIII.7 as a control class taken at random. Data collection is done by test technique. Collected data was analyzed using t-test at significant level α = 0,05, obtained tcount > ttable that is 3,48 > 1.67, so it can be concluded that there is significant influence of Think Talk Write (TTW) strategy to understanding of mathematical concepts student class VIII SMP Negeri 2 Lubuklinggau. The average score of students' understanding of mathematical concepts in the final test of the experimental class is 25.23 and the control class is 17.44. Keywords: Think Talk Write strategy (TTW), Understanding of Mathematical Concepts.