Introducing inorganic antimicrobial fillers is an effective strategy for addressing the susceptibility of polypropylene (PP) to microbial contamination. However, one notable challenge is the gradual decline in their antimicrobial efficacy due to the depletion of metal ions, the primary antimicrobial mechanism. In addition, the hydrophilic nature of inorganic filler surface results in incompatibility with the hydrophobic polymer matrix, potentially hampering their optimal performance. To overcome these issues, we employed surface modification of zinc silicate (ZS) glass powder using a series of silane coupling agents (#ACs), each featuring a quaternary ammonium group with varying alkyl chain lengths. This silanization systematically modulated the surface hydrophobicity of fillers, thus enhancing interfacial interactions with PP matrix and facilitating more uniform filler dispersion. Comprehensive analyses revealed that uniform filler dispersion significantly improves the overall performance of PP composites, especially antimicrobial activity due to effective release of zinc ions. Furthermore, the surface-modified ZS ensures long-term antibacterial effectiveness of PP composites through a dual mechanism, with the quaternary ammonium group providing complementary action even after zinc ion depletion. Consequently, this simple silanization using #AC successfully resolves the significant challenges of ZS, while simultaneously maximizing its effectiveness, resulting in a PP composite with robust and prolonged antimicrobial activity.