Consumer prices rose 1.7 percent year-on-year, said federal statistics authority Destatis in a statement.
This was markedly weaker than the 2.0 percent predicted by analysts and the 2.3 percent posted in November.
December's slowdown in price gains was down mainly to smaller bumps in energy and food prices.
Energy prices had climbed 4.8 percent in December compared to a leap of 9.3 percent in November.
And food prices rose just 1.0 percent, easing further from the 1.4 percent recorded in November.
In comparison, growth in rental prices held steady at 1.5 percent.
The data came after the European Central Bank announced the end of its “quantitative easing” programme that has seen it pump 2.6 trillion euros into the eurozone economy to stoke growth and inflation.
The ECB originally began buying debt in 2015, saying it wanted to fight the threat of deflation and keep money flowing around the eurozone economy.
Growth has picked up since then, surging in 2017 before falling back this year, but forecasts see inflation falling short of the central bank's target of close to, but below 2.0 percent.
According to the latest ECB forecasts, inflation for the eurozone should dip from 1.8 percent this year to 1.6 percent in 2019, before mounting back to 1.8 percent in 2021.