Firms sponsor the events for improving their image and strengthening their presence in market. As a commercial activity, sponsorship is largely used by corporates to reach new markets, increase awareness, and improve their image. Due to extensive use of social media by users and firms, Social media provides good opportunity to measure the effectiveness of sponsorship activities of firms. Sponsor's valence can be taken as measure for assessing the effectiveness of the sponsorship on social media. In this study, we aim to examine the impact of event reputation on the sponsoring firm's sentiment on social media. For achieving this, we selected two events: one with good reputation and second with bad reputation. Using twitter platform, we tracked the sentiment of those sponsors to see the effect of sponsorship and event reputation on sponsor's sentiment.