The uncertainty in an ESR age results almost completely from the error in the evaluation of the annual dose. In the case of corals, α-efficiency has a high influence on DE (Paleodose). The published kα-values vary from 0.05 to 0.2, so the correct determination of kα is crucial. In this experiment, based on direct irradiation with an 241Am-source, we used seven samples (20 aliquots for each sample) with different ages. The first aim was to improve the measurement conditions to reach a reliable data base for the α-efficiency calculation and the second was the question of age dependency of kα. With respect to the results of our experiments we propose an α-efficiency value for corals of 0.06–0.07 which leads to younger ages of about 7–10% less than with the kα factor of 0.05 we used in previous studies.