Polydopamine particles (PDAPs), a kind of biomimetic synthetic polymer, is found to be a multifunctional filler for isotactic polypropylene (iPP), which is one of the most important commercial resins. PDAPs not only possesses a high efficiency in nucleating â-form crystals but also shows an excellent thermal-oxidative stabilization effect toward iPP. The relative content of â-form crystals (Öâ) in nucleated iPP determined by differential scanning calorimetry reaches 75.4% when incorporating merely 0.5 wt.% PDAPs. The oxidation induction time (OIT) is 285% of that of neat iPP and the initial decomposition temperature (Ti) in air increases by 14.5°C when incorporating 1.0 wt.% PDAPs. Improved mechanical properties of iPP were also obtained upon adding PDAPs. The existence of local order structure in PDAPs possibly due to particularly ð–ð stacking of porphyrin-like tetramers are suggested to be responsible for the nucleating ability of PDAPs toward iPP. The ordered stacking model of three or more tetramers which meets the requirement of lattice matching theory of â-form crystals of iPP with a lattice misfit factor of less than 1.5%. Electron paramagnetic resonance (EPR) result suggested that the thermo-oxidative stabilization effect of PDAPs should be ascribed to the stable semiquinone radicals existed in PDAPs which can eliminate the free radicals promoting the degradation of PP.