Purpose <p>To develop a mesoporous silica nanoparticle-based delivery system for 4-phenylbutyric acid (4-PBA) and evaluate its potential to alleviate endoplasmic reticulum (ER) stress and improve mutant myocilin (MYOC)-associated glaucoma.</p> Materials and methods <p>We synthesized hollow/snowflake-like mesoporous silica nanoparticles loaded with 4-PBA (mSiO₂-PBA) for drug loading and release. Cellular uptake and cytotoxicity were evaluated in human corneal epithelial cells (HCECs) and human trabecular meshwork cells (HTMCs). The effects of mSiO₂-PBA on mutant MYOC secretion and ER stress-associated proteins were assessed by Western blot analysis. In Tg-MYOC^N450Y mice, ocular distribution of mSiO₂-PBA was examined by fluorescence imaging and high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). Therapeutic efficacy was evaluated by intraocular pressure (IOP) measurements, immunofluorescence analysis of MYOC accumulation and ER stress-associated markers in trabecular meshwork tissue, and transmission electron microscopy (TEM).</p> Results <p>mSiO₂-PBA exhibited efficient cellular uptake and favorable biocompatibility in vitro. Treatment with mSiO₂-PBA enhanced mutant MYOC secretion and reduced ER stress-associated KDEL-positive proteins in HTMCs. Following topical administration, mSiO₂-PBA achieved ocular penetration and exposure in trabecular meshwork tissue. In Tg-MYOC^N450Y mice, mSiO₂-PBA significantly reduced IOP, decreased mutant MYOC accumulation, and improved ER ultrastructural abnormalities in trabecular meshwork cells.</p> Conclusions <p>mSiO₂-PBA represents a promising nanoparticle-based delivery platform for 4-PBA in MYOC-associated glaucoma. By promoting mutant MYOC secretion and alleviating ER stress, mSiO₂-PBA demonstrated therapeutic efficacy in vitro and in vivo, supporting its potential as a nanotherapeutic strategy for MYOC-associated glaucoma.</p>