A method for the automatic design of a boiling water reactor (BWR) control rod (CR) pattern (CRP) was developed using the rank-based ant system, which is an effective optimization algorithm for a combinatorial optimization problem. The designed BWR CRP followed either the A2-B1-A1-B2 or the A1-B2-A2-B1 sequence in this study. After the CRP was determined, the SIMULATE-3 code was used to calculate the axial power distribution, the effective multiplication factor keff, the shutdown margin, and three thermal limits-which were then used to evaluate the CRP and update the pheromone concentration. The developed methodology was demonstrated using design CRPs for several fuel loading patterns, showing that the designed patterns can be obtained within a reasonable computation time and with an acceptable cycle length.