In archaeology a postpipe (or post pipe) is the term given to the remains of an upright timber placed in a posthole. Given the right conditions, timbers may survive over long periods of time and a recovered postpipe can simply be of solid wood. Under less preservative conditions however, only a dark circular stain of organic material may be left in the fill of the posthole observable in plan and section. This differs in consistency from the less organic backfill of the posthole and can be identified simply through this change in make-up. The size and depth and of the postpipe can provide information as to any reuse of the posthole especially if several different postpipes can be identified. They can also indicate the species of wood used and help suggest the nature of the structure that the timber once supported.

The term was first used by Maud Cunnington when she excavated the site of Woodhenge in the English county of Wiltshire during the 1920s and found numerous examples of decomposed timber posts.