In this study, we set an optimum blanching condition as a pretreatment condition to freeze welsh onion (Allium fistulosum L.) for the purpose of preserving the cooking material for long-term usage. With higher blanching temperature and longer processing time, the Hunter color values and the hardness of welsh onion tended to decrease, which confirmed softening of the tissue. Compared to before blanching, total bacterial counts decreased to near 2 log scale, whereas coliforms were not detected or decreased to a 1-2 log scale. Blanching by heating at 100 o C for 5 min decreased peroxidase inactivity to more than 94%, whereas only 47% of the inactivity was achieved at 80 o C for 1 min. The sensory evaluation for the blanched and defrosted welsh onion showed that the group blanched at 80 o C for 1 min was preferred significantly (p<0.05).

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