The A388 will be closed at Catsborough Cross junction near Frithelstockstone later this month while drainage improvements are carried out.
From Monday 17 July until Tuesday 25 July, the road will be closed between Monkleigh and Frithelstockstone and across the junctions between Torrington and Buckland Brewer.
The drainage upgrade will address a flooding issue on this stretch of the A388 and road surface patching work will be undertaken at the same time.
The road closure will be 24 hours a day and will include the weekend of Saturday 22 and Sunday 23 July.
A signed diversion will be in place via A388 Landcross, A386 Hatherleigh, A3072 Holsworthy, A388 and vice versa. Drivers with local knowledge are likely to find alternative routes.