The results of international large-scale assessments have shown that countries vary considerably in their mathematics performance. Culture has been suggested as a possible cause for the national difference, but insufficient empirical research has been conducted to investigate the effect of culture on mathematics achievement. Based on Hofstede's conceptualization of culture, the present study examined the relationship between national culture and students' mathematics achievement by analyzing data from 51 countries using two-level hierarchical linear modeling. The results showed that national culture played an important role in shaping mathematic achievement. It accounted for 23.89% of the country differences in mathematics performance after controlling for student gender, family socioeconomic status, and national GDP per capita. One cultural dimension "long-term orientation" had a strong positive association with mathematics achievement. The implication of the findings is discussed, followed by a discussion of issues regarding employing culture dimensions theory in mathematics education.