Results of failure of cylinders under the uniaxial compression are reported. Cylinders of three different diameters (37.5, 75, and 150 mm) were tested For all the cylinders, the height to diameter ratio was h/d = 2. The cylinders were made of microconcrete with maximum aggregate size 4.76 mm and the compressive strength (f(c)') of concrete was found between 34 and 48 MPa depending on the size of specimens. The concrete mix proportions of water:cement:aggregate:silica fume:superplasticizer were 0.3:1:4:0.1:0.08. The results reveal the existence of a significant size effect that can be approximately described by the size effect law previously proposed by Bazant. The experiments indicate that larger specimens tend to fail in a more brittle manner, while smaller specimens tend to fail in a less brittle or more plastic failure.