This paper focuses interest in science as one of the attitudinal aspects of scientific literacy. Large-scale data from the Programme for International Student Assessment (PISA) 2006 are analysed in order to describe student interest more precisely. So far the analyses have provided a general indicator of interest, aggregated over all contexts and contents in the science test (Organisation for Economic Co-operation and Development [OECD], 2007a; Prenzel, Schütte, & Walter, 2007).With its innovative approach PISA embeds interest items within the cognitive test unit and its contents and contexts. The main difference from conventional interest measures is that in most questionnaires, a relatively small number of interest items cover broad fields of contents and contexts. The science units represent a number of systematically differentiated scientific contexts and contents. The units’ stimulus texts allow for concrete descriptions of relevant content aspects, applications and contexts. In the analyses, multidimensional item response models are applied in order to disentangle student interest. The results indicate that multidimensional models fit the data. A two-dimensional model separating interest into two different knowledge of science dimensions described in the PISA science framework is further analysed with respect to gender, performance differences and country. The findings give a comprehensive description of students’ interest in science. The paper deals with methodological problems and describes requirements of the test construction for further assessments. The results are discussed with regard to their significance for science education.