In today’s world of rapid technological development one cannot deny the importance of collaborative writing systems. Besides many advantages of a collaborative writing system the major one is to allow its end users to work in collaboration with each other without having to physically meet. In the past various researches has been carried out for the usability evaluation of collaborative writing systems using the think aloud protocol method however there is no study conducted on the comparison of different usability evaluation methods in the context of collaborative writing systems. In this thesis work the authors have tried to find the limitations and capabilities of think aloud protocol and co-discovery learning methods in the context of a collaborative writing system called ZOHO, as well as the usability evaluation of ZOHO using think aloud protocol and co-discovery learning methods. The authors found various usability errors in ZOHO. Apart from this the authors also observed the two usability evaluation methods when they were used for usability evaluation of ZOHO. The authors found that both the methods have its’ own benefits and drawbacks. While the co-discovery learning method was fast enough, it was expensive in terms of human resource. On the other hand think aloud protocol method was slow to perform but there was less human resource used. Both the usability methods found almost the same usability errors. / In this thesis work the primary objective was to figure out the limitations and capabilities of think aloud protocol and co-discovery learning methods in the context of ZOHO; a collaborative writing system. Apart from this the secondary objective of this thesis was to conduct the usability evaluation of ZOHO and to find out what makes ZOHO ineffective, inefficient and unsatisfactory. The authors carried out usability tests on ZOHO using the think aloud protocol and co-discovery learning methods. After the tests results’ analysis the effectiveness, efficiency and satisfaction level of ZOHO was figured in section 7.2.1, 7.2.2 and 7.2.3 while the usability problems that make ZOHO ineffective, inefficient and unsatisfactory are discussed in section 7.2.4 of this thesis. Apart from the usability of ZOHO, the authors were also able to identify strong and weak points of the think aloud protocol and co-discovery learning methods when used for the usability evaluation of a collaborative writing system. They found that think aloud protocol testing is better if the evaluator is cost cautious or if he is looking for a detailed usability problems but does not cares about the time taken by the test. However if the evaluator cares about the test time and he cares less about the cost in terms of participants required for the test then he should use the co-discovery method for testing a collaborative writing system.