Twitter is used by different library types to communicate and engage with their community. This case study focuses on content choices in tweets and the level of engagement generated, in the context of two different types of library. The current study attempts to examine the contents of Library Twitter account of two libraries (academic and public) with the aim of evaluating in a comparative mode, their themes and levels of user engagement. This research used a mixed method research approach. For quantitative approach, this study analyzed 100 Tweets from each library, i.e. RMIT University Library and State Library of Victoria. Also, the study analyzed a number of tweets and levels of engagement by recording numbers of likes, replies and retweets. The qualitative aspect analyzed each Tweet to determine engagement level and type of content shared by each library. The results demonstrate that the public and academic libraries publish different types of content. The varied nature, audience and mandate of each library appear to influence the focus of their tweets. Also, the results show that the level of engagement is a factor of the numbers of tweets in any theme. The limitation of this study is the data set contained only 100 tweets for each library. Moreover, the number of users and registered library accounts had probably increased since the study was conducted.