Weathering transforms fresh un-weathered rock into saprolite and soils, porous materials that may hold availablewater for plants and nutrients. The conjoint characterization of mineral weathering and development of porosity is helpful in understanding rock weathering and the development of soil.The objective of this study was to investigate mineralogical transformations and the increase in total porosityduring granodiorite weathering in South Brazil by combining petrographical observations, mineralogical analyses, and porosity measurements. The studied granodiorite profile presented a saprock of ~2 m thickness with spheroidal weathering, a ~15 m thick saprolite of and soil of ~2 m thickness. The intensity of weathering wasestimated using chemical indices (CIA and WIS) and by the production of fines particles of silt and clay sizes. Asweathering increased from saprock to saprolite and soils total porosity increased from 1.73 % in the unweathered rock, between 3.57 and 10.5 % in the saprock and 11.02 % in the saprolite. The chemical losseswere limited in saprock and saprolite (CIA = 68, Δ4Si = 29.31 %) and increased in the topsoil (CIA = 85.73,Δ4Si = 56.83 %), indicating a moderate weathering intensity. Petrographic observations by optical microscopeand SEM, chemical composition using SEM-EDS and X-ray diffraction results showed principal mineral weatheringreactions were the transformations of biotite into vermiculite (with biotite/vermiculite mixed layers asintermediate weathering stages) and weathering of plagioclases and potassic felspars into kaolinite. The multimineral composition of the saprolite indicated a progressive transformation of primary minerals withincreasing weathering intensity. The results show that the opening of the porosity is likely to control thedevelopment of the weathering and should deserve more detailed characterisation.