Westpac Bank is the newest member of the elite $100 billion club, boasting a market capitalisation of $100.9 billion after a broad stock market rally.
It's the second bank to jump over the hurdle this year after Commonwealth Bank, whose market capitalisation has continued to rise and is about $115 billion.
Discounting BHP Billiton's London shares, Commonwealth Bank is now the biggest stock on the Australian market.
Since the start of the year, Commonwealth Bank has rallied 15.3 per cent, Westpac is up 24.8 per cent. In terms of market caps, Commonwealth and Westpac are ranked the 10th and 11th largest banks in the world, with ANZ coming in at 14th ($82.2 billion). National Australia Bank is slightly behind, ranked at 16th with a market cap of $76.7 billion.
Combined, the big four are expected to notch more than $13 billion in combined profits as they start reporting first-half results in coming weeks.
Australia's biggest banks have among the highest credit rankings in the world, and remain just a handful to carry the "AA" credit rating.
Market report — Page 27