Future Fund grows to $140.8 billion

The Future Fund has grown to $140.8 billion as of end-March, adding $80 billion since its conception in 2006.

Future Fund chairman Peter Costello warns the long-term investment outlook remains challenging. (AAP)

A strong global economy has helped the Future Fund grow to $140.8 billion, but its chair Peter Costello has warned the long-term outlook remains challenging.

The fund, created in 2006 to help pay for superannuation liabilities of public servants, has exceeded all of its benchmark timeframes - for example, returning 8.5 per cent over 10 years compared to a target of 6.7 per cent.

Releasing a portfolio update for the March quarter on Monday, the fund said investment returns had added more than $80 billion to the $60.5 billion in original contributions made by the former Howard government, in which Mr Costello was the treasurer.

No further contributions have been made since 2008.

Mr Costello said sustained economic growth across the major advanced economies had been a positive for the investment environment but the longer-term outlook remained challenging.

"Looking forward, the board remains alert to a range of uncertainties and risks, including the response of central banks to the changing economic environment, international political tensions and the potential for shocks to the investment market," Mr Costello said in a statement.