The value of the Government's assets has jumped nearly $40 billion since 2008 - but its liabilities have almost doubled.
At the end of 2013, the Government had $244.4 billion in assets and $174.4 billion in liabilities.
The Treasury said both would grow, in its first investment statement outlining what the Government owned and what it owed.
By 2018, it forecasts assets will be worth $279.9 billion and liabilities $181.6 billion.
The Treasury said the balance sheet was worth three times the value of the publicly listed companies on the Stock Exchange.
Treasury deputy chief executive Vicky Robertson said the Government needed to do a better job managing its assets and liabilities.
"The balance sheet is really large. It's complex. It's growing. What we own and how we manage it is really critical to the services that taxpayers get out of the assets on our balance sheet," she said.
"How these are funded is really important and, at the end of the day, this matters really for New Zealand's living standards."
Better management would create opportunities for governments to spend more on services, such as health and education, or cut taxes, she said.