The New Zealand Superannuation Fund had a record 25.8% return for the 12 months to the end of June.
The fund, often referred to as the Cullen fund, is now worth $23 billion, up from $19 billion a year ago.
Guardians of New Zealand Superannuation chairman Gavin Walker said the fund's performance over the past year has been exceptional and should not be seen as a precursor of ongoing returns.
Chief executive Adrian Orr said the fund's strong performance was due to a heavy weighting towards growth assets, including global equities, and from higher valuations of domestic assets such as Kaingaroa and Z Energy.
As the fund is not scheduled to pay out any money until the 2030 financial year, Mr Orr said it remains focused on long-term, growth oriented investment strategies.
Since its inception in September 2003, the fund has achieved an 8.8% annual return.