Alkali-Activated Ceramsite Concrete (AACC), a novel green building material, is important for the reutilization of industrial waste. Although there has been considerable progress in research on AACC, further investigation is still needed on ceramsite size, early strength, etc. In this paper, 11 groups containing 198 standard cubic specimens were fabricated to investigate the effects of water-binder ratio, alkali mass fraction and ceramsite diameter on compressive strength and splitting tensile strength at different ages. And the slump constant of the mixtures was tested for different water-binder ratios and alkali mass fractions during fabrication. The results showed that the slump and strength increased with the increase of water-binder ratio. As the alkali mass fraction increased the slump decreased and then increased but the strength increased and then decreased. Therefore the proper value of alkali mass fraction was about 6%. When the diameter of ceramsite increased, the compressive strength first increased and then decreased. Thus the 5–15 mm diameter was the optimum. Splitting tensile strength always decreased with the increase of diameter of ceramsite.