Chemical weathering (dissolution) rate of rhyolites from Kozushima over 52000 years of weathering determined by a field-based study was lower than those obtained by a laboratory dissolution experiment by a factor of 12-1000. In order to perform a reactive transport modeling to bridge the field and laboratory rates, detailed characterizations of the reaction and transport properties of the rhyolite were conducted. Hydraulic conductivity and diffusion coefficient were significantly affected by the degree at which pores were saturated with water, whereas reactive surface area was relatively unaffected. The modeling revealed the followings: (1) Owing to temporal decrease of dissolution rate associated with a change of solid surface reactivity, whole rock dissolution rate decreased with time and approached to the ‘field rate’ in relatively early stage of weathering; (2) Saturation index (proximity to chemical equilibrium) was large at the initial stage of weathering but became smaller as weathering proceeded.