The damage behavior of the potting materials around a pinhole, being used in the mechanical joints of sandwich composites, is investigated experimentally. The sandwich composite panels used in the tests were manufactured by the vacuum-assisted resin infusion technique. Each of the top and bottom face sheets of the panels consisted of two woven E-glass/epoxy layers. As the core material, PVC foam (AIREX (R) C70.55) was used. The potting material consists of an epoxy resin and hardener system mixed with short E-glass fibers (4 wt%). The diameter of the potting material D and the edge distance to the center of pinhole E were considered as the two main varied dimensions. They were chosen as D = 10, 12, 15, and 18 mm and E = 15, 20, and 25 mm. The damage mechanisms of the potting material and sandwich sections are presented by using load-displacement variations and images of the damaged samples, subjected to in-plane pin loading.