The effect of flakiness, one of the shape property of aggregate on concrete, is not an issue sufficiently clarified. In addition, there are no satisfactorily detailed limitations for flakiness on a global scale. This study, in which limestone was used as an aggregate, describes the dependence of flakiness on the concrete behaviour both in the fresh and hardened state. In this context, slump tests in the fresh state and compressive strength tests in the hardened state at 7, 28 and 60 days were carried out using concrete mixes prepared in the same design and with different fl akiness percentages. An increase of flaky particle fraction in coarse aggregate caused flocculation and segregation leading to the inhomogeneity of concrete mix. The slump of the mix decreased markedly as the flakiness increased, and an increase in flakiness by 25% resulted in an average reduction of 18 mm in the slump value. The test results indicated that the compressive strength of concrete decreased significantly with increasing flakiness. According to these negative linear relationships with strong correlation coefficients, an increase in the flaky coarse particles by 25% led to a decrease in compressive strength of average 0.9, 0.4 and 1.2 MPa for the curing times of 7, 28 and 60 days, respectively. Furthermore, the increase in flakiness enhanced particularly the range and standard deviation of compressive strength values with the same flakiness percentage, which this trend was most pronounced and meaningful at 60 days. This phenomenon exhibits that the differences and uncertainty in the compressive strength of the concrete specimens with the same flakiness percentage, increase distinctly with the increase in the flakiness.