The visit comes after an invitation extended by government last year.
The diplomats will visit four companies, Mbada, Marange Resources, Diamond Mining Corporation (DMC) and Anjin. They will also visit the ZRP Diamond Base.
On Wednesday, the diplomats will visit Arda Transau where families from the diamond fields are relocated.
Diamonds from Marange have courted controversy amid calls by civil society organisations that there is no transparency in the marketing of the gems.
Finance minister Tendai Biti has been complaining that Anjin has not been remitting money to treasury. Anjin is a joint venture between the Chinese and the Zimbabwe Defence Industries.
Biti has said despite claims that the Zimbabwe Mining Development Corporation (ZMDC) owns Anjin, the state entity had no equity in the diamond producer.
However, ZMDC general manager, Jerry Ndlovu told the diplomats Monday the state entity had 10% percent shares.
Revenue from diamonds is set to contribute US$600 million to fiscus this year.