This paper investigates the feasibility of using the P-wave velocity measured by the impact-echo technique to estimate the strength of hardened self-consolidating concrete. The relationship between the through-transmission ultrasonic pulse velocity (UPV) and the strength of high performance concrete was established previously by performing experimental studies on water-cured cylinders made of concrete having variations in water-cementitious amterial ratio and aggregate content. However, the through-transmission UPV measurement is not applicable to concrete elements with only one accessible surface. In this paper, two plate-like specimens were made of self-consolidating concrete and they had different curing conditions. One specimen was immersed in water and the other was covered with wet gunny sack for 7 days. The impact-echo technique, one-sided wave velocity measurement technique, is adopted to determine the P-wave velocity of the plate-like concrete specimens at an age of 28 days. The difference between the impact-echo P-wave velocity (IE-PV) and the through-transmission ultrasonic pulse velocity (UPV) is studied. In addition, the measured IE-PV is used to estimate the strength of the plate-like concrete specimen and the estimated strength is verified by taking cores from the specimen.