Due to environmental (low CO2 emission) and economic benefit, supplementary cementit1ous materials (SCMs) have been widely used in reinforced concrete structures.However, the question from engineering practice is to which extend these blended mixtures do meet the future durability criteria.Chloride ingression is nowadays considered as the main concern for reinforcement corrosion.Due to self-desiccation or drying process,cement-based materials are no longer saturated, which would greatly influence the chloride transport properties.This paper explores the effect of water saturation level on chloride diffusivity in cement-based materials by resistivity measurements.Experiments were performed on mortars made of different blended materials, i.e.fly ash, blast furnace slag and limestone powder.Mortar materials have been curing for 200 days conditioning in humid room at 20±1℃, followed by oven drying at 50℃ until the samples reach targeted water saturation levels.The results showed that chloride diffusivity is highly dependent on the water saturation level and water-vapour desorption isotherm of the mortar material.The dependency varies with cement type, and is significantly related to pore size distribution characteristics.In addition, the effect of water content on chloride diffusivity is more evident in blended cement mortars than reference ordinary Portland cement mortar.For the materials studied in this research, the capillary pores with diameter range of 7.1-73 nm plays dominated role in chloride diffusion under non-saturated state.