US consumer prices fell 0.3 percent in November, much more than forecast, even as declining oil prices were expected to cause a contraction, Labor Department figures showed Wednesday.
The prices of food and services were higher, but the 3.8 percent fall in energy prices from October more than offset those rises.
Economists had expected a fall of just 0.1 percent in the overall consumer price index.
Stripping out volatile food and energy prices, the core CPI rose 0.1 percent in the month, in line with forecasts.
Year-on-year, inflation was just 1.3 percent, compared with 1.7 percent in October.
Factoring out food and energy costs, annual inflation was 1.7 percent.
Food prices gained 0.2 percent in the month, shelter and transportation services both rose 0.3 percent, and medical care services increased 0.4 percent.
The slowdown in inflation eases pressure on the Federal Reserve to raise interest rates from the zero-level where they have sat for six years. The Fed completes a two-day policy meeting later Wednesday in which it is expected to update the outlook for tightening monetary policy in the coming year.