Microblogging has recently become a new form of communication that is rapidly changing everyone’s life. Through services such as Twitter, millions of people can broadcast short messages to their followers via instant messaging, SMS, or web interfaces. However, few studies have been conducted to understand the impact of these emerging phenomenons. In this study, we seek to understand the social consequences of microblogging. Further, we want to examine which aspects of microblogging are related to the consequences. We recruited 120 undergraduates and randomly assigned them to one of four groups (29 to 31 participants in each group). Each group was asked to perform a microblogging task at least once a day for a month. The tweet-only group was asked to tweet without reading others’ tweets (they did not follow others). The tweet-and-read group was required to post a tweet and read others’ tweets (they followed each other). The read-undergrad-only group read the tweets generated by the tweet-only group. The read-nonundergrad-only group read tweets from a pre-selected group of non-undergrad twitter users. We created these groups to understand the consequences of different aspects of microblogging (i.e. regular read-and-tweet, tweet-only, read tweets from people in the same community, and read tweets from people outside one’s own community). Participants completed a battery of surveys (including PANAS, subjective well-being, loneliness, communication, and peer attachment scales) before and after the microblogging treatment. Our results showed that after one month, the tweet-and-read group had a higher level of positive affect (measured by PANAS) than the other groups. The tweet-only group, on the other hand, considered themselves having better communication and relationship with their friends (measured by subscales of the Inventory of Parent and Peer Attachment) than the other groups. This research is the first empirical study that employed a between subjects design to systematically understand the social consequences of microblogging. Results suggest that both writing and reading microblogs are needed to improve one’s affective state. More interestingly, simply writing microblogs is sufficient to make one perceive or experience better communication and relationship with others.