The sale offered further encouragement for the eurozone's fourth-biggest economy, which last year resisted speculation that it would need a sovereign bailout to rescue its public finances.
Overall demand for the 12- and six-month Spanish treasury bills was €10.9 billion , more than double the government's upper target of €four billion ($5.2 billion), the central bank said in a statement.
The rate of return demanded by investors who bought €1.013 billion of six-month bills fell to 0.492 percent from 0.530 percent in the last comparable sale on April 16.
Investors also bought 3.034 billion euros' worth of 12-month bills at a rate of 0.994 percent, down from 1.235 percent on April 16.
The treasury was also in the course of carrying out an auction of benchmark 10-year bonds in a syndicated sale to a group of banks, the economy ministry said.
After a turbulent 2012, indicators of confidence in Spain have strengthened over recent months.
Its borrowing costs have fallen since the European Central Bank (ECB) announced in September its readiness to act to curb borrowing costs for troubled member states that accept strict conditions.
The economic outlook remains dark however. Spain has been in recession since late 2011 and is not expected to emerge from it until next year. The unemployment rate has soared past 27 percent.
Other data on Tuesday showed that the net debt owed by Spanish banks to the ECB fell for the eighth month running in April to reach its lowest level in a year.
It was €257.2 billion in April, down from a peak of 388.7 billion reached in August, the data from the bank of Spain showed.
Higher debt to the ECB indicates greater difficulty for banks to raise financing on the markets — another key indicator of financial confidence in the country.
The figure remains relatively high, having surged over the past two years of financial trouble from €42.2 billion in April 2011.