Interest rates on 30-year fixed-rate mortgages averaged 4.85 percent for the week ending March 26, down from the previous week's 4.98 percent.
The rate broke the previous record low of 4.96 percent set 10 weeks earlier, according to Freddie Mac.
The 30-year fixed-rate mortgage is the lowest since Freddie Mac started the Primary Mortgage Market Survey in 1971.
"The Federal Reserve's announcement that it intends to purchase Treasury securities over the next six months caused bond yields to drop and mortgage rates followed," Frank Nothaft, Freddie Mac vice president and chief economist, said in a statement.