<p>This study investigates the unfired and fired microstructural characteristics of Jin Zhuan (imperial bricks) from the Ming–Qing period, using materials excavated from the Yuanhetang kiln site in Suzhou, China. Employing a combination of X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), and mercury intrusion porosimetry (MIP), the mineralogical composition, microstructural evolution, and porosity changes associated with the imperial brickmaking process were analysed. The unfired samples exhibited a fine-grained, silicate-rich clay body, while the fired bricks showed evidence of significant densification, sintering neck formation, and a more uniform pore network. Comparison with historical texts, such as Zaozhuan Tushuo and Gusu Zhi, highlights the intricate artisanal techniques developed to optimise brick performance. Our findings provide new scientific insights into the material transformations underpinning the renowned durability and quality of Jin Zhuan, offering valuable references for future conservation, heritage reproduction, and material science research.</p>