The corpus contains 668,529 tweets (tweet IDs) relevant to "impact investing", accompanied by sentiment labels given by an automated sentiment classifier. Impact investing involves investments made into companies, organizations, and funds with the intention to generate social and environmental impact alongside a financial return. The tweets relevant to impact investing were collected in the period from March 28, 2017, to January 28, 2018, through the Twitter Search API, and annotated for sentiment labels "Negative", "Neutral" or "Positive" by a general-purpose English language sentiment classifier. The tweets were collected based on a list of known impact investing Twitter users, relevant keywords and impact investing related events. In particular, the queries include relevant users (@YF_Academy, @esmeefairbairn, @resonanceltd, @Big PotentialSI, etc.), single hashtags (#socfin, #impinv #socialfinance, #impactinvestment, etc.), combined hashtags (#social & #finance, #social & #investment, #impact & #assessment, etc.), and hashtags of major impact investing events (#impact2, #socap17, #OxfordIIP, #skollwf, etc.).