Hydrotalcites as flame retardants for industrial applications require good compatibility with polymers. Glycerin co-solvent was employed during the precipitation of MgAl hydrotalcite (Mg/Al-HT) particles and the dispersion of the Mg/Al-HT particles in a polypropylene (PP) matrix was studied. The microstructures, textural and surface properties of the hydrotalcites were contrastively investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, laser particle size analysis, Barrett–Joyner–Hallender/Brunauer–Emmett–Teller methods (BJH/BET), and thermogravimetric and differential thermal analysis (TG-DTA) as well as pH_zpc analyses. The results suggested that the interactions between the co-solvent and the Mg/Al-HT affected the nucleation, resulting in the variation of crystallinity. The employment of glycerin co-solvents during the nucleation was conducive to the combination of crystal water with the brucite sheets. The hydrotalcite (mix-MHT) obtained by adding glycerin co-solvent during the nucleation possessed the smallest particle sizes with the narrowest size distribution and the most hydrophobic particle surfaces, which made the mix-MHT particles disperse uniformly throughout the PP matrix due to their good compatibility with PP. The improvement of the compatibility between the particles and the polymer was mainly caused by the decrease of the hydrophilicity on the surface of the particles due to the presence of glycerin in the interlayer spaces of the mix-MHT particles. The insertion of the mix-MHT particles into the PP matrix could also significantly enhance the thermal stability and maintain the mechanical properties of PP, and the mix-MHT had the best performance as a flame retardant with the PP matrix.