The A$2.33 billion ($2.5 billion) surplus handily topped market forecasts of A$1.9 billion and took the 12-month total to a record A$23.4 billion.
"The trade sector is a 'bright spot' for the economy," said George Tharenou, a senior economist at UBS. "This captures the nominal income boost coming into the economy from very high commodity prices and hence the terms of trade."
That was a reminder of why the Reserve Bank of Australia (RBA) remains upbeat on the longer-term economic outlook despite weakness in some sectors like retail and housing.
The Reserve Bank of Australia left the official cash rate unchanged at 4.75 percent Tuesday for the seventh time since November -- the last time they were raised -- saying it now believed domestic growth was "unlikely to be as strong as earlier forecast."
Globally, the bank said headwinds had grown, with banking and sovereign debt problems in Europe stoking uncertainty and volatility.
The RBA has cautioned that rates are still likely to rise at some point to contain inflation, though markets are betting it can hold off for the rest of the year given softness in some parts of the economy outside of mining.
Australia's exports rose 3.2 percent in May to A$25.7 billion, from April, led by a near 50 percent increase in gold shipments to A$1.6 billion. That was the fifth highest on record with over half the gold going to the UK.
Coal exports were up 3 percent, continuing their slow recovery from flooding in Queensland earlier in the year, while exports of farm goods rose 6 percent.
Imports edged up by 0.4 percent in May to A$23.9 billion. Shipments of vehicles from Japan continued to recover from earthquake disruptions, while imports of capital goods were pulled down by a drop in aircraft purchases.
Australia's terms of trade — what it gets for exports compared to what it pays for imports — soared over 22 percent in the year to March to the highest in at least 140 years.
Going by the RBA's own measure of Australian commodity prices, yet further gains look likely for the second quarter. Its index of prices climbed 10 percent in the quarter, from the first quarter, to be up 28 percent for the year.
That meteoric run was mainly thanks to higher prices for iron ore and coal as demand from China and India outstrips supply. For the 11 months to May, goods exports to China expanded by no less than 42 percent to A$58 billion.
While growth in the emerging giants has cooled somewhat, miners are confident the industrialization of more than two billion people will last for decades yet and are investing with that in mind.
A record A$430 billion ($451 billion) in resources investment is either underway or on the drawing board in Australia, a real stretch for an economy with an annual output of A$1.3 trillion.
Miners plan to spend A$83 billion in 2011/12 alone, though such is the rush that many are struggling to find everything from workers to housing, trucks to tires.
