Language is embedded in a particular culture and learners inevitably learn about its culture while learning a language. The integration of cultural contents in ELT (English Language Teaching) materials is strongly related to the current status of English. Being a global and commonest language, many recent theories suggest that the cultural contents of English materials should not be limited to native English-speaking countries and should include local cultural contents. To this end, this research is aimed at investigating the existence of cultural contents in an English textbook used by Senior High School students grade X in Indonesia, entitled Bahasa Inggris. To this purpose, the media of cultural presentation, categories of culture, and aspects of culture were investigated. The method used in this study was content analysis. Some underlying models proposed by Cortazzi and Jin (1999), Moran (2001), Yuen (2011), and Xiao (2011) were used as the main framework for analyzing the textbook. The investigation revealed that: (1) cultural contents were mostly presented through pictures and reading texts (61%), (2) the dominant aspect of culture is products (44%), and (3) the presented culture were mostly about source culture (45%). In summary, the exposures of visible cultural aspects of Indonesian culture which were presented through pictures and texts dominated the exposures of culture in Bahasa Inggris. Based on the findings, it is a need for textbook developers and teachers to provide a more balanced proportion of cultural contents in terms of the dimensions (products, practices, persons, perspectives) and categories of culture (source, target, and international target cultures) to help learners develop their intercultural understanding. 
Keywords: language and culture, cultural contents, English textbook