Electrospun starch fiber mats have many potential applications, but an improvement in their mechanical properties is required to realize them. In the present study, wet-electrospun starch fiber mats were subjected to post-drying conditioning at controlled equilibrium relative humidity and equilibration time. The weight-normalized ultimate tensile strength of starch fiber mats increased significantly with equilibration at relative humidity > 0.75 after 28 days. Morphological observation and X-ray diffraction analysis excluded significant changes in fiber size or crystallinity, and thus we concluded that conglutination brought about by the plasticizing effect of water and observed microscopically was primarily responsible for this mechanical improvement.