The present study evaluated pore surface fractal characteristics of high-strength cement pastes with different ground granulated blast-furnace slag (GGBFS) replacement ratios. Using the results of mercury intrusion porosimetry measurements, the surface fractal dimension in various pore-size ranges was calculated. Experimental results show that the fractal characteristics appeared in mesopores in range of 6-10 nm and 10-25 nm and larger capillary pores with sizes of more than 100 nm. In larger capillary pores, as the GGBFS replacement ratio increased up to 65%, the surface fractal dimension and pore volume decreased, and they increased when the GGBFS replacement ratio increased from 65% to 80%. In contrast, higher GGBFS replacement ratios in mesopore regions resulted in an increased surface fractal dimension and pore volume. Furthermore, in the regions where fractal characteristics appeared, pore volume and the surface fractal dimension exhibited a proportional relationship. The ratio of the surface fractal dimension to the volume of larger capillary pores was strongly correlated with the compressive strength of the specimens. (C) 2017 Elsevier B.V. All rights reserved.