In this study, the efficacy of bacterial antagonists was tested in both pre- and post-harvest stages against Botrytis cinerea, which causes one of the major diseases of strawberries. In total, 219 bacterial antagonists were obtained from various parts of strawberry plants, and their efficacies against B. cinerea were determined. Two isolated bacteria, which were identified as Bacillus megaterium and Pseudomonas vesicularis, were found to be effective and otherwise suitable as biological control agents. Moreover, an isolate of Pseudomonas fluorescens from pea plants was successfully used against B. cinerea in the experiments. These three antagonist isolates were field-tested in both the pre- and post-harvest periods in two consecutive years. The field studies demonstrated that all three isolates were as effective as a synthetic fungicide. In the first year field tests, the isolates reduced the decay incidence to 41.08-43.03 % compared with 55.48 % in the control. Similar results were obtained in the second year. In the post-harvest stage, all the bacterial isolates also controlled the disease effectively. The bacterial population was monitored in both the pre- and post-harvest periods using a spontaneous antibiotic-resistant mutant and the RAPD-PCR method. The RAPD-PCR technique alone proved insufficient to determine the population levels of the bacterial antagonists.