The authors experimentally studied the size effect of axial compressive properties of concrete cube and slenderness ratio of 2:1 prism with cross-section side length of 100mm to 800mm in this paper. Commercial concrete was used for test specimens. Specimens were cast and cured outdoors. To highlight the size factors, accumulation of sand on the end surface of the specimen was used to eliminate the end cyclo-hoop effect. The test results show that, in the case of eliminating the end restraint, failure modes of the prism and the cube are the same. There isn’t determined relationship between the cubic compressive strength and cylinder axial compressive strength of concrete, in the case of the specimen slenderness ratio not more than 2 to 1. However, the decline trend of cylinder axial compressive strength with size is slightly greater than the cubic strength. Fly ash concrete, ordinary concrete without fly ash and fiber reinforced fly ash concrete show different size effects. Size effect for concrete with 40% fly ash replacement of cement significantly reduced. The experimental results also show that, strength, elastic modulus and ultimate strain of concrete are all size-dependent. But there are different size effect trends between strength and deformation properties. Ultimate strain of concrete decreases as size increases, and more attention should be taken to this point.