The average 30-year fixed mortgage interest rate fell from 3.4 percent with an average 0.6 points to 3.36 percent, Freddie Mac said.
A year earlier, interest rates for 30-year, fixed-rate loans were at 3.94 percent.
For 15-year loans, interest rates dropped from 2.73 percent to 2.69 percent with an average 0.5 points. A year ago, 15-year loan rates averaged 3.26 percent.
Rates for 15-year loans even dropped below the rate for five-year adjustable rate loans, which has not occurred since October 2009, Freddie Mac said.
Average interest rates for five-year adjustable-rate mortgages rose from 2.71 percent in the week with 0.6 points to 2.72 percent. In the same week of 2011, rates for five-year ARM contracts stood at 2.96 percent.
The average interest rates for one-year ARM contracts was 2.57 percent in the week with 0.4 points, down from 2.6 percent in the previous week.
Rates a year ago for one-year ARM contracts averaged 2.95 percent.
Rates fell "due to the mortgage purchases by the Federal Reserve and indicators of a weakening economy," said Freddie Mac vice president and Chief Economist Frank Nothaft.