The important role of language, including reading, on student performance on assessments in school academic areas such as mathematics has been addressed in number of studies. Although positive relations between different aspects of reading and mathematics performance have been investigated, there have been few studies focusing on the interaction between the context of the mathematics item and student reading proficiency, and most of those there were related only to the verbal loading. Recently, a low correlation between verbal loading and item difficulty was found for PISA mathematics items. This study used PISA 2003 mathematics data with 41 countries with about 275,000 students. Item response theory (IRT) was used to detect differential item functioning (DIF) in mathematics items related to reading ability.