Electronic textbooks (e-textbooks) provide great convenience to teachers and students in both being activity-oriented and having more than one media in it. Especially during the COVID-19, e-textbooks have become much more important than any other time for the effective teaching of online courses. Therefore, many publishers rearranged e-textbook versions of their printed publications in Turkey. Regarding human-computer interaction, making the usability tests of these e-textbooks will give ideas to e-textbook content developers. Thus, three of these e-textbooks were carefully analysed for this research. They are the products of Kurmay, Speed Up and YDS publishing houses. The study was carried out with seven voluntary English teachers who teach 8th grades, work at the Ministry of Turkish National Education and have at least 3 years of teaching experience. Due to the pandemic, the sessions were held online by using the 'Zoom Meetings', which is an online meeting software. The usability was analysed according to effectiveness, efficiency and satisfaction principles of the International Organization for Standardization (ISO). At the end of the test, it was observed that the usability of Reading Alley and Marathon Plus e-textbooks were high and the usability of Speed Up was very high.