A barnstar (or barn star) is a decorative painted object or image, often in the shape of a five-pointed star but occasionally in a circular "wagon wheel" style, used to adorn a barn. They have no structural purpose, but may be considered lucky, akin to a horseshoe mounted over a doorway. They are most commonly seen in German-American farming communities.

Barnstars were meant to represent the mark of the builder, but became more frequently used for aesthetic purposes and were added to the building after construction was complete. Enthusiasts have traced a number of wooden barnstars to individual builders in the Pennsylvania area, where numerous examples can still be seen.

Barnstars were used in the United States during the 18th century and as late as 1870 in Pennsylvania, where their popularity increased greatly following the Civil War. Their regular use preceded that time, however, and stars were commonplace on large buildings, particularly factories, in pre-war Richmond, Virginia.

Barnstars remain a very popular form of decoration and modern houses are sometimes decorated with simple, metal, five-pointed stars which the makers describe as "barn-stars". They are often deliberately distressed or rusted, alluding to the traditional decoration.