The Bank of Spain says bad loans at the country's banks, a key indicator of their financial health, jumped to 6.19% in February, the highest level since September 1995.
The bad loan rate was 6.06% in January, which was the highest level since November 1995.
Spain's lenders, especially its regional savings banks that account for about half of all lending in the country, have been heavily exposed to bad debt since the collapse of the property sector at the end of 2008.
Moody's last month downgraded Spain's credit rating by one notch to Aa2 and warned it may do so again on fears the government will be unable to meet its targets of slashing the public deficit and on concerns over the cost of restructuring the banking sector.
Spain's finances and economy, with a jobless rate of just over 20% the highest in the industrialised world, have prompted fears it may need a costly EU bail-out like Greece, Ireland and Portugal.
But markets have shown renewed confidence in the Spanish economy recently, as evidenced by the lower yields on government bond sales.
The government has strengthened bank balance sheets, cut spending and pursued economic reforms to allay market jitters over the outlook for Spain's finances.
Under government regulations announced last month, the banks must raise the proportion of core capital they hold to 8% of total assets from the current 6%, or to 10% if they are not listed on the stock exchange.
