We report on the experimental study of an anomalous transmission effect in ultrathin metallic gratings, where the metal thickness is much thinner than the skin depth. In particular, incident transverse magnetic polarized waves are reflected while incident transverse electric polarized waves are transmitted. This anomalous effect is strongly dependent on the metal thickness and metal width. We systematically investigate and demonstrate the anomalous effect and find the optimized nanostrip thickness and width by introducing a shadow-mask fabrication approach. Our results demonstrate the possibility of developing ultrathin nanostrip based planar metasurfaces with low loss.