The index, which has posted gains for 10 of the past 12 months, dropped 0.1 of a percentage point after rising by 0.5 percent in November.
The index slipped to 108.2 with a decline in three of seven components that make up the headline index, the Conference Board said.
The index uses 2004 as a base year, assigning it the value of 100 to provide a reference point for comparisons.
The Coincident Economic Index, which measures current business conditions, rose in December, climbing 0.3 percent to 105.9.
"Taken together, the U.K. LEI suggests a moderate pace of economic recovery over the next few months. Also, concerns about emerging markets performance are likely to dampen the outlook for businesses and investors," said Conference Board economist Bert Colijn.