Daily mining revenue and gross profit fell for a third consecutive month in September, the report said.
The bank noted that the network hashrate rose 2% from August.
Daily block reward gross profit fell to the lowest "on recent record" in September, the bank said.
The average bitcoin {{BTC}} price and the network hashrate rose slightly in September, while daily mining revenue and gross profit fell for a third straight month, JPMorgan (JPM) said in a research report Tuesday.
The hashrate rose for the third month in a row, adding 2% from August to 643 exahashes per second (EH/s). Hashrate refers to the total combined computational power used to mine and process transactions on a proof-of-work blockchain.
JPMorgan estimated that miners earned an average of $42,100 per EH/s in daily block reward revenue last month, 6% less than the month before.
"We estimate daily block reward gross profit declined 6% month on month (m/m) to $16,100 per EH/s (38.4% gross margin) in September, the lowest point on recent record," analysts Reginald Smith and Charles Pearce wrote.
Transaction fees were subdued and didn't reach more than 5% of the block reward, the authors noted.
The total market cap of the 14 U.S.-listed miners tracked buy the bank rose 4% to $21 billion. Hut 8 (HUT) outperformed with a 21% gain last month, and CleanSpark (CLSK) was bottom of the pile with a 13% decline.
Bitcoin's annualized volatility was 44% last month, a drop from the 62% seen in August, the report added.
Read more: Bitcoin Mining Profitability Remains at All-Time Lows as Prices Fall, Hashrate Rises, JPMorgan Says
