Although release profiles of drug from hydrophilic matrices have been well recognized, the in-depth mechanism of drug has not been characterized. In this paper, drug release mechanism was elucidated based on hydrodynamic gelling process, release of carrier and atomic distribution of formulation components. A matrix tablet consisting of hydroxypropylmethylcellulose (HPMC 6, 4,000 and 100,000mPa∙s), chlorpheniramine maleate (CPM) as a model and fumed silicon dioxide (Aerosil® 200) was prepared via direct compression. The distribution of atoms and HPMC imagingwere characterized using scanning electron microscope (SEM)/energy-dispersive X-ray spectroscopy (EDX), and near-infrared (NIR) analysis, respectively as a function of time. A texture analyzer was also used to characterize the thickness and maintenance of gel layer of HPMC matrix tablet. The HPMC matrix tablets showed Higuchi release kinetics with no lag time against the square root of time.High viscosity grades of HPMC gave retarded release rate because of the greater swelling and gel thickness as characterized by texture analyzer.According to the NIR imaging, low-viscosity-grade HPMC (6 mPa∙s) quickly leached out onto the surface of the tablet, while the high-viscosity-grade HPMC (4000 mPa∙s) formed much thicker gel layer around the tablet and maintained longer via slowerosion, resulting in retarded drug release. The atomic distribution of the drug (chlorine, carbon, oxygen), HPMC (carbon, oxygen) and silicon dioxide(silica, oxygen) and NIR imaging of HPMC werecorresponded with the dissolution behaviors of drug as a function of time.The use of imaging and texture analyses could be applicable to explain the release-modulating mechanism of hydrophilic HPMC matrix tablets.