This study focused on the extrinsic and intrinsic motivation levels of eighth grade students and its relationship with their mathematical achievement. The participants of the study included 6,829 students who took TIMSS in 2011 and 239 mathematics teachers. The data obtained from the student and teacher questionnaires that are included in the content of TIMSS exam were used. Two-level HLM was used to examine how students' mathematics achievement is related to their extrinsic and intrinsic motivation levels. One way ANOVA with Random effects, Means as Outcomes Regression Model, The Random Coefficient Regression Model were used in the two level HLM. The study results show that students' mathematics interest, self-efficacy, perceptions of mathematics, and the frequency of mathematics exams and teachers' interest in students at schools are related to mathematics achievement. The examination of the effect size of the variables particularly shows that intrinsic motivational variables have a stronger relationship with mathematics achievement than extrinsic motivational variables. The overall analysis of the study findings shows that mathematics achievement is related to both intrinsic and extrinsic motivational resources that need to be addressed by mathematics experts and teachers.