This paper documents three business cases of social impact investing (SII) for marginalized communities in Hong Kong. Target stakeholders of the cases include displaced old tailors, elderly and wheelchair-bound people, and single-parent families. They are all privately-owned and profit-driven entities with their own social missions. Information on the cases is collected from structured interviews and meetings with their founders and stakeholders. The paper further discusses general issues of SII in Hong Kong and possible mechanisms to support SII development. Tax exemption for investors and donors, related government subsidy schemes, certification on social impacts, and establishment of social impact funds would help SII business thrive in the future.