The S&P/ASX200 had climbed as high as 8,285.2 at 11.32am AEST on Monday, eclipsing the previous intraday record of 8,246.2 set on September 20.
At midday, the benchmark index was up 61.4 points, or 0.75 per cent, to 8,273.6, while the broader All Ordinaries had gained 61.2 points, or 0.72 per cent, to 8,538.0.
Moomoo analyst Jessica Amir said September had brought out the bulls, despite it traditionally being the weakest month for stocks.
The rally has been supported by gains in the price of iron ore and other commodity metals following China's announcement last week of massive stimulus measures to revive its lagging economy.
Also in the US, the Federal Reserve's preferred measure on inflation came in slightly weaker than expected in a monthly readout Friday night, supporting further aggressive rate cuts.
Eight of the ASX's 11 sectors were higher at midday, with telecommunications down 0.3 per cent and the bourse's two consumer sectors both basically flat.
The energy sector was the biggest gainer, up 2.0 per cent, possibly responding to the threat of a broader Middle East war impacting oil supplies after Israel's killing of Hezbollah leader Hassan Nasrallah.
Woodside was up 2.7 per cent and Santos had climbed 2.0 per cent.
In the heavyweight mining sector, goldminers were losing ground near even as the precious metal traded near a record high of $US2,658 an ounce.
Northern Star was down 1.2 per cent, Newmont had dropped 3.0 per cent and Evolution had fallen 1.9 per cent.
Elsewhere in the sector, BHP was up 1.9 per cent, Fortescue had climbed 3.0 per cent and Rio Tinto had gained 2.1 per cent.
All of the big four banks were higher, with CBA up 1.2 per cent, NAB gaining 1.6 per cent and Westpac and ANZ both adding 0.3 per cent.
Star Entertainment Group was up 19 per cent to 29.75, clawing back some of Friday's 44.4 per cent plunge.
In currency, the Australian dollar was buying 69.17 US cents, from 68.86 US cents at Friday's ASX close.
The Aussie breached the 69 US cent level briefly at times late last week, reaching as high as 69.37 US cents late on Friday, but otherwise hasn't traded above 69 US cents since February 2023.
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