The billionaire's company piled more than $13 billion into those stocks in the quarter, making Berkshire a major shareholder in four of the five largest US banks, according to a regulatory filing Wednesday.
The JPMorgan stake deepens the bank's ties with Berkshire Hathway.
Buffett, 88, has always been one of the most influential bank investors and has been diversifying his bets in the industry. The firm also added to its stakes in Bank of America and Goldman in the third quarter.
Buffett may be betting that a stronger US economy and rising interest rates will benefit the nation's biggest lenders.
Apple shares are down 17.25% in the same time, so its no wonder that Berkshire is wearing a near $10 billion loss on the value of its Apple stake, despite increasing it in the quarter.
Berkshire also said it bought smaller stakes in another bank PNC Financial, as well as insurance company, Travelers.
The billionaire investor has been struggling to find large acquisitions to put a more-than $100 billion pile of cash to work.
Berkshire also spent $928 million repurchasing its own stock in the quarter. Five of Berkshire's ten largest holdings by market value were banks, including Bank of America, Wells Fargo, U.S. Bancorp and Goldman Sachs, according to CNBC. But the big news is that he's bonkers for bank stocks.
Mr. Buffett previous year said Berkshire would sell shares in the scandal-riddled bank because it needed to keep its holding below the 10% threshold at which the Federal Reserve can exert oversight over a bank shareholder.
Buffett, Combs and another portfolio manager, Ted Weschler, handle Berkshire's investments. But Buffett said in 2012 that he had a personal investment in the bank run by Jamie Dimon.
The Travelers stake represents a rare bet on an insurer that competes with Berkshire's own Geico unit. The final 1.4 million holding disappeared in the September quarter.
Berkshire's biggest holding, Apple Inc., is a relatively new one that has swiftly climbed to the highest spot in its more-than $207 billion stock portfolio. Two years ago, Buffett's company disclosed that it was piling into the iPhone maker after years of typically avoiding investments in technology companies.