The optimized RAPD-PCR conditions, which can be utilized as a basic information for the analysis of the genetic characteristics were investigated with four onion varieties, named Changryungdaego, Yeoeuijuhwang, Yakwangju, and Dabonghwang using Operon primers, OPR01 (TGCGGGTCCT) and OPZ20 (ACTTTGGCGG). We tested several concentrations of DNA, primer, and MgCl2, annealing temperature, number of PCR cycle, and presence/absence of pre-heating time at the begining of PCR reation in the 25${mu}ell$ volume. The best RAPD profiles were obtained using 50ng of DNA, 5mM of primer, 1.5mM of MgCl2, 45$^{circ}C$ of annealing temperature and an absence of pre-heating time. An establishment of the stable and reproducible RAPD-PCR conditions are expected to be useful for the subsequent RAPD-related investigation, such as genetic characterization of the onion strains, re-establishment of phylogenetic relationships and development of new varieties.