This study evaluated the progressive deterioration of concrete mixtures containing various proportions of ground-granulated blast-furnace slag (GGBFS) and silica fume (SF) caused by sulfate attack under tropical climatic conditions. The water-binder ratio (w/b)--0.40 and 0.50), moist curing period (3 days, 7 days, and 28 days), and fineness of GGBFS (4,500 sq cm/g, 6,000 sq cm/g, and 8,000 sq cm/g) were the other experimental variables. Concrete prisms were immersed in a 5% sodium sulfate solution for 32 weeks and periodically monitored for the change in flexural strength and linear expansion. The experimental results were compared with those of ordinary portland cement (PC) and sulfate-resisting portland cement (SRPC) concrete specimens. Results demonstrated that the resistance of GGBFS concrete is a complex function of w/b and proportion of GGBFS in the mixture. The 65% GGBFS mixture of 0.5 w/b, which was moist cured for 7 days and 28 days, showed initial signs of deterioration. The same mixture with a w/b of 0.40 and a moist curing period of 3 days indicated superior resistance to sulfate attack. This trend was also true for 100% OPC concrete mixtures with w/b's of 0.40 and 0.50. The concrete mixtures incorporated with greater proportion of GGBFS showed greater resistance to sulfate attack, irrespective of w/b and moist curing period. A similar trend was also true for concrete mixtures with SF (5% and 10%) and 100% SRPC concrete. For a given proportion of GGBFS (65%), there was no consistent trend between the extent of deterioration and the fineness of GGBFS. For all the mixtures investigated, the moist curing period had little influence on their resistance to sulfate attack. The observed sulfate-induced deterioration was due to the formation of poorly crystalline ettringite.