Epistemological beliefs (EB) play a vital role in students' performance (Buehl & Alexander, 2001, 2006; Fives & Buehl, 2004; Lodewyk, 2007). The paper was designed to examine the relationship between students' EB about the Mathematics curriculum and their academic achievement (marks) at the secondary level. Eight hundred and ten participants (girl students) were selected through cluster random sampling technique from public-sector secondary schools of Lahore District. The Mathematics inventory prepared by Grouws (1994) was adapted to identify the secondary school students' EB regarding the Mathematics curriculum that was comprised of seven sub-scales. Students' academic achievement was gained from their Mathematics score obtained in grade IX. In data analysis, the Pearson Product-Moment Correlation was applied to identify the association between girl students' EB and their academic achievement. The result showed that students' EB regarding the Mathematics curriculum positively correlate with Mathematics academic achievement at the secondary level.