More than 20 years after the first round of the OECD's Programme for International Student Assessment (PISA), it has become one of the most important large-scale international assessments, at a global level and in particular in Europe. Thus, a growing number of scholars have examined or discussed its research design. Nonetheless, a key feature of PISA seems to have been less examined by critical works: the "discourse of the research" in the PISA literature. Indeed, the PISA reports appear to be scientific literature, both in textual form and in terms of the intentions expressed. Based on the reports published by the OECD since 1999, this article examines, in line with the French tradition of discourse analysis, the characteristics of research writing in PISA and the explanations of its conceptual approach, test design or result analysis. This analysis shows the differences between the research discourse in PISA and typical scientific rhetoric, particularly in terms of constructing a contradictory theoretical dialogue or a discussion of the limits of its approach. Finally, the article questions how these differences indicate a particular construction of education research within PISA and its possible relationship with the global or European dynamics of this scientific field.