Strength of concrete had been given more significance in past but no attention was paid on durability of concrete. Further it is recognized that strength of concrete alone is not sufficient. Resistance against harshness of environmental conditions to which the concrete is exposed over its entire design period is also equally important. Generally, permeability is one of the parameters of durability of concrete. At the aggregate-paste interface, porous transition zones are formed which affect the pore size distribution. In the initial stage, micro cracks are so small that may not cause higher permeability. But the drying shrinkage, thermal shrinkage and externally applied load causes propagation of micro cracks with time. Permeability is the responsible factor for volume change. Ca(OH)2, a by-product of hydration of cement paste of concrete can be reduced so that the concrete pore structure is to be densified. Therefore, the present investigations are done on High Volumes of Slag Concrete which consists of Cement: GGBFS in the ratio 50:50. Cylinders were cast for different water binder ratios (0.55 to 0.27). The Chloride permeability is tested for 28 days, 90 days and 180 days of curing. The Chloride permeability was observed to be very less in the case of specimens cured for later ages.