The utilization of Linz-Donawitz (LD) slag in cementitious applications has gained traction due to its widespread availability, offering a potential solution to reduce global warming. This study evaluates the impact of particle size fractions on the chemical, mineralogical, and dissolution characteristics of LD slag. Nine particle size fractions were analyzed, revealing significant variations in oxide content based on particle size. While CaO, Fe2O3, and SiO2 contents remain similar in higher (þ500 μm and þ1,000 μm) and lower (þ3 μm) size fractions, particles between þ3 μm to þ75 μm exhibit a 1.5% free lime content. Quantification using XRD-based Rietveld refinement indicates LD slag primarily consists of crystalline phases (quartz, calcite, portlandite, brownmillerite, wustite, and belite) alongside an amorphous phase, with amorphous content ranging from 40% to 60% across all sizes. The þ3 μm size fraction exhibits the highest belite, brownmillerite, and wustite content, with comparatively lower free lime content than other size fractions. Dissolution analysis in an alkaline environment shows a slightly improved dissolution behavior with decreasing particle size from þ150 μm to þ3 μm. Calcium exhibits higher initial dissolution rates than iron and silicon within the first three hours, with silicon becoming more prominent after twelve hours. Overall, this study offers a comprehensive analysis of the correlation between particle size and chemical/mineralogical composition, highlighting the potential for converting industrial waste into ecofriendly products.