OSLO- The deputy central bank governor in charge of monitoring Norway's $1.1 trillion sovereign wealth fund will step down before the end of his term, Norges Bank and the finance ministry said on Wednesday.

The surprise resignation of Egil Matsen comes just as the central bank is also preparing to pick a new chief executive for the fund, the world's largest of its kind, to replace long-serving CEO Yngve Slyngstad. 

Commonly known as the oil fund, it invests close to 70% of its funds in global equities, owning stakes in about 9,000 companies. Some 28% is invested in a portfolio of fixed-income assets, while unlisted real estate holdings make up the rest.

Matsen, a professor of economics who was appointed in November 2015 for a six-year term, said he will move back to Trondheim, some 400 km (250 miles) north of Oslo, to be able to spend more time with his family.

"I have had a very interesting job, and it has been a privilege to work alongside so many capable colleagues to perform a vital public mission," Matsen said in a statement.

The finance ministry separately said the aim was for Matsen to stay in his post until a replacement had been found.

The current term of the central bank's other deputy governor, Jon Nicolaisen, expires on April 1 next year, and the two appointments will be seen in context, the ministry added.

"Matsen does his job very well and is an important link between (the finance ministry) and the central bank board. I would have preferred that he stayed longer, although I understand his need to prioritise differently," Finance Minister Siv Jensen said.

Established since 1996 to save petroleum revenue for future generations, the size of the fund has grown to almost three times that of Norway's annual gross domestic product, far exceeding original projections. 

(Reporting by Terje Solsvik, editing by Louise Heavens and David Evans) ((terje.solsvik@thomsonreuters.com; +47 918 666 70))