Open-source software is becoming a gradually more popular as a software development method; some of the most successful softwares are for example: the Linux operating system, Mozilla, Apache web server and openoffice.org. Open source softwares viewed by many as being very good in terms of their usage, reliability, performance and market share. Mostly open source software developer focus on functionality and different feature of the software; on the other hand they ignore the user centric design requirement. In this thesis the importance of the usability in Open source applications, such as Openoffice.org are described and how usability can be measured by assessing user performance such as, satisfaction, effectiveness and acceptability. Openoffice.org is a freely available office suite in different operating system and with different languages. The OpenOffice.org 3.0 feature set is similar to the feature set of Microsoft Office 2003. It has word processing, spreadsheet and presentation applications all together within a common suite. But still this application suite is not much familiar among common users that cause a major usability threat for usability studies. The basic purposed of this thesis was to find out the issues and users satisfaction regarding this Openoffice.org. Empirical method of usability assessment such as thinks aloud, Questionnaires and interviews were used.