This study used several electronic-book (e-book) displays (a conventional LCD under transmissive mode, a conventional LCD under reflective mode, a Ch-LC display, and an e-ink display) to investigate the effect of e-book inclination (105° and 1 35°) and ambient illuminance (200, 800, 1500, and 2200 lux) on the comprehension of subjects. Results indicate that the ambient illuminance does not significantly affect the comprehension of subjects. However, their comprehension differed significantly when using different e-book displays. In addition, the interaction between illuminance and e-book display had a significant effect on their comprehension. When the ambient illuminance was set at 800,1500, and 2200 lux, the subjects'comprehension for reading different e-book displays did not show a significant difference. When the ambient illuminance was set at 200 lux, however, their comprehension for reading a Ch-LC display, an e-ink display, and a conventional LCD under transmissive mode were better than their comprehension of reading a conventional LCD under reflective mode. Regarding the inclination for using e-books, the subjects'comprehension was better under 105° than that under 135°.