Physicochemical and emulsification properties of dialdehyde starch nanocrystals (DASNCs) and dialdehyde starch nanoparticles (DASNPs) were measured in this study. The starch nanocrystals (SNCs), which are prepared by sulfuric acid hydrolysis, were oxidized by sodium periodate to obtain the DASNCs. The DASNPs were prepared by gelatinization and alcohol precipitation of dialdehyde starch. After oxidization by sodium periodate, the SNCs and SNPs became smaller and more suitable for dispersion. X-ray diffraction results showed that the crystal pattern of the SNCs was preserved after oxidation. However, only a single broad peak at the Bragg angle of the DASNPs was observed. The SNCs and DASNCs can form Pickering emulsions, but the emulsions stabilized by the SNPs and DASNPs could be easily broken. The preparation methods for the two kinds of dialdehyde starch nanoparticles are different, so their structures, properties and applications are different.