Combined sales at department store chains run by Hyundai Department Store, Lotte Shopping and Shinsegae Co fell 1.1 percent in March in annual terms, the Ministry of Trade, Industry and Energy said.
Earlier estimates from the finance ministry had shown sales had edged up 0.1 percent from a year earlier. Sales in February had fallen 1.7 percent year-on-year.
The trade ministry attributed March's decline to fewer holidays in the month compared with a year earlier as well as cold weather that resulted in less spending on clothing.
On a quarterly basis, department store sales rose 1.1 percent and at the fastest speed since a 2.4 percent rise in the third quarter of 2013, the data showed.
Meanwhile, sales at the country's top discount stores fell a revised 3.7 percent, versus an earlier estimate of a 3.8 percent decline.
The data comes just before the Bank of Korea releases its preliminary estimates for first-quarter growth, for which analysts have forecast a seasonally adjusted 0.8 percent rise from the previous quarter.