The aim of this study is to evaluate the usability of the mobile application of Centralized Hospital Appointment System (CHAS) developed by the Ministry of Health in 2012, as part of e-government efforts in Turkey. A study group was formed consisting of 16 people, 8 females and 8 males between the ages of 18 and 55, and selected for their CHAS experience. Qualitative and quantitative methods were used as part of a mixed research design. Qualitative data sources for the study consisted of observation notes taken while performing authentic tasks that were selected through field research, notes generated by the think-aloud method and meeting notes taken after the process. Quantitative data were collected with a performance evaluation form and questionnaire. Researchers analyzed the data using SPSS 21 program for the quantitative data, and using Microsoft Word and Excel for the qualitative data derived from the participant group. Descriptive analysis, nonparametric chisquare test (single sample with two variables) and Kruskal-Wallis H Tests were used for the quantitative analysis of the data. Moreover, a content analysis method was used for the qualitative analysis of the data. Results of the data analysis indicated that participants of both male and younger groups performed better than others, which was significantly distinctive and matched other literature related to the usability of technology in the many tasks performed by the application. In addition, participants who had experience of using touch-screen devices and were of higher educational status were found to be statistically significantly more successful than other participants. Findings derived from the study indicate that the general specifications and interface of the CHAS mobile application are beneficial and necessary for accessing the medical services. Conclusions also suggest that the application would be easier and more effective to use after the suggested revisions have been made.