Increase of specific surface area by mechanical activation accelerates hydration reactions of cements and results in higher compressive strengths. The compressive strength development of chemically activated high phosphorous slag content cement at different Blaine finenesses has been investigated. Mixes of phosphorous slag (80 wt.%), Portland cement (14 wt.%), and compound chemical activator (6 wt.%) were prepared at different Blaine finenesses using a laboratory ball mill. Compressive strengths of mortar specimens cured in lime-saturated water were measured at different curing times. Results show that increasing fineness to 450 m(2)/kg, provides the possibility of achieving high 28-day compressive strengths up to almost 93 MPa. Complementary measurements confirmed that increasing fineness results in significant reductions in the amount of water absorption and the total open pore volume of mortar specimens. The simultaneous application of both chemical and mechanical activations, therefore, provides complementary improving effects in the quality of high phosphorous slag content cements. (C) 2013 Elsevier B.V. All rights reserved.