The　effect　of　CaO　and　MgO　content　on　the　compressive　strength　(CS)　and　flexural　strength　(FS)　of　alkali-activated　slag　mortar　(ASM),　which　was　activated　by　NaOH　(Na2O%　=　4%),　was　investigated.　The　pore　structure　of　alkali-activated　slag　paste　was　investigated　via　mercury　intrusion　porosimetry　(MIP).　The　morphology　of　ASM　was　observed　by　field　emission　scanning　electron　microscope　(FSEM).　The　study　shows　that　the　CS　and　FS　of　ASM,　which　was　activated　by　NaOH,　increase　first　and　then　decrease　with　the　improvement　of　CaO　and　MgO　content.　The　optimal　CaO　and　MgO　content　for　CS　are　both　9%　of　the　slag　mass.　The　CS　of　ASM　with　optimal　CaO　and　MgO　content　can　achieve　46.54MPa　and　47.79MPa,　respectively.　The　optimal　CaO　and　MgO　content　for　FS　are　6%　and　3%　of　the　slag　mass,　respectively.　The　FS　of　ASM　with　optimal　CaO　and　MgO　content　can　achieve　11.23MPa　and　11.11MPa,　respectively.　The　comprehensive　mechanics　performance　of　ASM　are　the　best,　when　the　CaO　content　is　6%.　©　Content　from　this　work　may　be　used　under　the　terms　of　the　Creative　Commons　Attribution　3.0　licence.