The purpose of this study was to investigate the effects of onion on the physicochemical, microbiological and sensory properties of Dongchimi. Dongchimi with levels(0, 5, 10, 20%) of onion was fermented at twodifferent temperatures : Group A was fermented at 4$^{circ}C$ and group B was fermented at 4$^{circ}C$ after fermentation at room temperature(27$pm$0.5$^{circ}C$) for 24 hours. During the fermentation up to 45 days, total acidity increased while pH decreased gradually. Total acidity of group B was relatively higher than that of group A. The content of reducing sugar was reached the maximum value in 6 days of fermentation in the group A and on 3 days in the group B. Especially, the highest content of reducing sugar was shown on the Dongchimi added with 5% onion in the group A and 20% onion in the group B. Vitamin C was reduced in the early stage of fermentation, and increased gradually after 10 days. However, vitamin C of Dongchimi without onion increased rapidly in the early stage of fermentation and remarkably decreased thereafter. After 20 days, vitamin C was maintained in Dongchimi added with 10% onion of both two groups. The number of lactic acid bacteria was reached the maximum value on 1 day in the Dongchimi without onion and on 3 days in the Dongchimi added 5, 10 and 20% onion of group A, while gropu B was reached on 1 days and then decreased thereafter. As a result of the sensory evaluation, Dongchimi added 5% onion in the group A showed the highest scores in texture and overall acceptability. Whereas, in the group B, Dongchimi added 20% onion was the most preferable one.