Synthesis and nucleation ability of a novel silsesquioxane‐based β‐nucleating agent for isotactic polypropylene (iPP) are presented. A silsesquioxane cage (POSS) was octa‐functionalized with a commercially used nucleating agent, namely N2,N6‐dicyclohexylnaphthalene‐2,6‐dicarboxamide (NU‐100), and used as a carrier with the ability to promote crystallization of β‐phase in polypropylene matrix. Presented results include the synthesis route of the β‐nucleating agent (SF‐B01) and a description of its nucleation ability in iPP. The influence of SF‐B01 on iPP matrix was examined using differential scanning calorimetry, wide‐angle X‐ray scattering and static tensile tests. Investigations were complemented with polarized light optical microscopy upon non‐isothermal crystallization of composites as well as scanning electron microscopy to qualitatively assess the filler distribution. Polypropylene samples modified with different amounts of NU‐100 were used as reference. Modification carried out with both nucleating agents reveals their comparable efficiency, i.e. a structure rich in β‐phase is obtained in both cases. © 2016 Society of Chemical Industry