Abstarct: Due to the significant role of textbooks in transferring cultural content and developing interculturally competent learners, a large body of research in Iran has been focused on evaluating cultural representations in various textbooks, but a diachronic content analysis is neglected. Therefore, this study examines three English textbooks taught at Iranian high schools (Graded English 3, English Book 3 and Vision 3) in terms of their cultural representations. These hidden cultural representations of cultural facts will be discovered through Peircean Semiotics approach which is a tool for analyzing content. The findings revealed that the curriculum developers hold opposing views on the concept of culture during the last fifty years. Although the representation of national cultural items in Graded English 3 was satisfactory, more than a half of the items (54.40%) was dedicated to the target culture. English Book 3 contained a smaller number of items compared to Graded English 3, and baxsed on data analysis, it was majorly concentrated on Islamic culture especially in its visuals which goes very well with the aims of the book. Finally, Vision 3 only attempted to introduce Iran's national culture (55.67%), but it was not successful since it presented important signs out of context and under-represented them.