This paper illustrates a strong bond between the genre constitutions of reading textbooks and the improvement of EFL learners` reading proficiency arising therefrom. Textbooks should be as simple as possible within the proficiency level of EFL learners. The advisability of simplified and authentic texts is recommended for their reading texts. Authentic simple texts should be devised or located in the real world. Peering into whether reading texts contain simple, suitable, exploitable, and readable contents, which should be a desideratum on an authentic textbook, this paper argues that only when reading texts are properly constituted to encompass EFL learners` interest in English, a genuine learner-minded activity in which students focus on the class can be implemented. In a bid to nail the key elements of the reading textbooks, this paper analyzes their components and contexts based on several genre categories. Along with the belief that reading texts should contain the genres to advocate considerable attention to EFL learners with intermediate-level reading proficiency and to encourages them to move on to a higher-level proficiency, this paper claims that the genres of reading textbooks should not swing too far one way, but the constitutions should be kept in equilibrium.