The magnetization reversal process in microfabricated FePt (0 0 1) dots with a diameter of 250 nm is experimentally investigated based on phenomenological analysis. The initial and minor magnetization curves show that the magnetization reversal of the FePt dots is dominated by the nucleation of reversed domains. The phenomenological analysis of the coercivity (H c) gives the defect regions for nucleation as 26 4 nm and 18 6 nm for the FePt dots before and after annealing, respectively. The reduction of the defect regions after annealing is in agreement with the enhancement of H c for the annealed dots. Micromagnetic simulations also show the reduction of Hc due to the existence of defects in a dot, which is consistent with the experimental results.