Total industrial output fell 0.6 percent, after a minimal 0.1 percent rise in February.
The March drop was double what analysts expected.
Utilities output slid 5.9 percent, largely reversing February's increase that was weather-related.
Mining output fell for the third straight month, but by a smaller 0.7 percent.
Manufacturing eked out a 0.1 percent gain after two months of declines.
Compared with a year ago, industrial output was up 2.0 percent in March.
As industrial output slowed, capacity utilization fell for the fourth month running, hitting 78.4 percent, well below the long-run average of 80.1 percent.