3i has agreed to but 100 per cent of the shares in business Mizuho Investment Management (MIM).
MIM specialises in the management of funds raised to invest in senior and subordinated corporate debt, providing investment advisory services in return for fees.
It has 28 staff and has rub eight funds totalling more than £4bn since 2005 and had £3.7bn of assets under managementat 31 March 2010.
3i's existing debt management activities will be merged with MIM to form a distinct business line, 3i Debt Management.
Jeremy Ghose, chief executive officer (CEO) of MIM will become Managing Partner and Chief executive of 3i DM and will join 3i's leadership team.
3i group chief executive Michael Queen said: "There is an excellent cultural fit with 3i and the expanded business will create an enhanced debt platform to grow profitably into the future."