A new conductivity cell, developed previously, was employed from 15 to 250 degrees C, in an effort to investigate the inter-relation between the measured conductivities and the solution chemistry of high-temperature H2SO4-Al-2(SO4)(3) solutions. These electrolytes exist in the laterite leach slurry of the pressure acid leaching process. It was found that, at 250 degrees C, the effect of Al-2(SO4)(3) on conductivity decreases with increasing Al-2(SO4)3. This is in agreement with our previous findings that aluminum mostly forms Al(SO4)(+) at low molalities, whereas 85% of aluminum is associated as Al-2(SO4)(3)(0) at near-saturation molalities. At 250 degrees C and constant H2SO4 molality, the solution conductivity drops with increasing Al-2(SO4)(3) molality. It is suggested that this drop is caused by a sharp decrease in ionic equivalent conductivities of H+, HSO4-, and Al(SO4)(+) This drop was found to be similar in nature to the drop when H2SO4 is added at very low concentrations. A new unified correlation for ionic equivalent conductivity in terms of one-third power of individual ionic strength was found. Finally, a simple mixing rule was developed to calculate the ionic equivalent conductivities in H2SO4-Al-2(SO4)(3) solutions.