Total production in the mining, manufacturing, gas and electricity industries in Asia's fourth-largest economy inched up 0.1 percent from December, Statistics Korea said.
The growth rate was down from an unusually high 2.4 percent on-month expansion in December.
Compared with a year earlier, January's output shrank 3.8 percent. Because of the Lunar New Year holidays, January had 22 working days this year, compared to 24 days in 2013.
Production of memory chips and semiconductor parts made by firms such as Samsung and SK Hynix fell 4.7 percent on-month in January, while auto production by the likes of Hyundai and Kia rose 6.7 percent.
Production of mobile phones and TVs -- the country's key export items -- increased 9.5 percent from the previous month.
Production in the service sector rose 0.9 percent on-month and expanded two percent from a year earlier, the report showed.
The South's export-reliant economy grew 2.8 percent in 2013, and the central bank has forecast a 3.8 percent expansion in 2014.