We report the observation of an enhanced stimulated emission from optically pumped GaN nanopillars. The nanopillars were fabricated from an epitaxial wafer by patterned etching followed by crystalline regrowth. When the sample was optically excited, a strong stimulated emission peak emerged from a broad spontaneous emission background. The emission was attributed to electron-hole plasma gain at high carrier density. The emission slope efficiency was greatly enhanced by 20 times compared with a GaN substrate under the same pumping configuration. We remark that the enhancement is due to better gain and photon interaction from the multiple scattering of photons among nanopillars.