The company has acquired the three-storey building on Copse Walk which is partially occupied by the Royal Collage of Nursing and Cardiff Diagnostics. The building was originally developed and sold by the company.
The Cardiff office of Savills acted on the acquisition of the property and retained agent Fletcher Morgan is marketing the vacant space within the building.
Tony Fletcher, managing director of Cardiff Gate, said: "We are happy to be reinvesting in old stock where we see plenty of long term growth. It allows us to refurbish the building to current standards and also gives us some immediate vacant stock."
Cardiff Gate is home to 75 companies including Scottish & Southern Energy, Lloyds Banking Group and The Number 118 118 and 4,000 members of staff.