This paper reports the results of an investigation on the chloride diffusivity of volcanic pumice (VP)-blended hardened cement pastes with varying curing age of up to 1 year. The pastes had 0, 20 and 40% VP as cement replacement and water to binder ratios (W/B) of 0·40, 0·50 and 0·60. The accelerated chloride ion diffusion test was used to calculate the chloride ion diffusion coefficient (Di) of pastes using the Nernst–Plank equation for steady-state condition. In addition, electrical resistivity, mercury intrusion porosimetry, and differential scanning calorimetry (DSC) tests were also conducted. Good correlations were found between Di, total pore volume and electrical resistivity of the pastes. The Di values of VP-blended pastes were within the range of 10−7–10−9 cm2/s. It was also found that blending cement with VP significantly reduced the long-term chloride ion diffusion coefficient and hence increased the long-term corrosion resistance of pastes. This fact was also supported by the presence of lower quantity of Ca(OH)2 and higher quantity of Friedel's salt in the VP-blended pastes as observed from the DSC tests. Pastes with 40% VP showed better performance in terms of chloride ion diffusivity. The water to binder ratio was also found to affect the Di at the early ages of curing, but became less important at the later ages of curing.