The figures, from the Spanish central bank, showed the debt fell again in April.
The figures indicate that the eurozone country's banking system is weaning itself off massive special refinancing support provided by the ECB at the height of its economic crisis and property market crash which hit the banks.
At one point, eurozone leaders were worried that Spain might need a national bailout which would stretch the capacity of rescue systems to the limit.
But Spain managed to avoid a rescue along the lines obtained by Greece, Ireland and Portugal, although its banking system was propped up in various ways, by the ECB but also with funding from the eurozone.
The eurozone package took the form of help totalling more than €40 billion ($55.0 billion) for the weakest banks and for Sareb, a special entity created to offload the most toxic bad property loans and assets, and to dispose of them.
The latest figures show that the commercial banks are increasingly able to finance themselves normally on the open market, just as borrowing rates for the Spanish government have also dropped sharply as the eurozone crisis fades.
The net debt owed by Spanish banks to the ECB now stands at €182.4 billion down from €257.2 billion at the end OF April last year. and from €183.5 billion in March.
At the worst point, this bank debt totalled €388.7 billion in August 2012.
Since then it has fallen steadily, but still remains extremely high.
Spain, which has the fourth-biggest economy in the eurozone, emerged in the third quarter of last year from its second recession in five years, and in the first quarter of this year the economy grew by 0.4 percent.
But against the improving background for some indicators, the unemployment rate remains extremely high at 25.93 percent.
The population is suffering from the effects of radical measures to cut the public budget deficit and to make the economy more efficient so as to raise exports.
The banks have restricted loans to businesses and to individuals, and many economists and international organisation say that this is weighing on the fragile recovery.