A variety of healthcare applications have been introduced so far. For the success of such applications their usability plays a significant role. The more the application is user friendly and easy to use the more percentage it will get to be adopted by the consumers. This work reviews and evaluates range of mental health applications in terms of their usability. There are some approaches that could prove to be best usability indicator for the mobile apps and can determine how well their functionalities work. Some of the major approaches to usability testing are user testing, surveying, A/B testing and expert based evaluation. The usability testing has explored the missing factors in usability of the mental health related mobile apps. At the start, all the data related to mobile health apps is collected according to which an excel sheet is prepared. The excel filecontain all the necessary information (name, language, date of release/latest update, availability on Android or iOS, availability as freeware or in-app purchase, cost, availability as lite-version, number of downloads/ installations, user rating, number of user ratings, availability of an interface/connectivityto (an) external sensor(s)/ devices and type of external sensor(s)/ devices) . The study has figured out the range of functions supported in each mental health apps that includes information about disease function, add/remove more than one patient diary, scheduling function, advisory function/ therapy support, treatment, diagnosis/symptoms, messaging, result tracking/ graph creation /visual representation and treatment adherence/rewards. After data collection usability testing is performed in a closed environment. A team of 6 members (3 male, 3 female) performed usability test on 10% of collected apps. In usability testing the major factors analyzed is comprehensibility, presentation (image and text), affordability, efficiency and error rate. The analysis is performed to observe effects of some factors (like range of functions, platform effectiveness, etc.) on usability of mobile apps and see if these factors affect app usability in a positive or negative manner. It is observed that the number of mental health apps available in Android is much more than those available in iOS. However, the user rating of iOS apps is higher than that of android. It is noticed much improvements can be made to increase the usability of mobile health apps. For instance, by providing help related functions, increases the understandability of various app?s features and hence can increase user interaction and app?s usage time. Similarly, if apps icons are meaningful they can grasp users? attention easily. The paper has discussed in detail the positive and negative features of mental health apps in both platforms.