This study was estimated for cabbage aphid, Brevicoryne brassicae in Brassica campestris L. var. rapa (L.) Hartm. in order to institute of Economic injury levels(EILs). B. brassicae was innoculated on April 29, in differently 0, 5, 10, 20 and 40 adults per ten plant, respectively. After inoculated of B. brassicae, the density was increased until harvest ing gradually in all plots except non innoculate plot. and Higher inoculation density were increased higher than lower inoculation density. Percentage of damage leaf was higher in plots with higher initial aphid density than in plots with lower initial aphid density. And the leaf weight of commodity were decreased in higher initial aphid density. The decreasing rates of leaf weight of commodity was increased with increasing initial aphid density. The relationship between initial B. brassicae densities and the decreasing rates of leaf weight of commodity was well described by a linear regression, Y=0.8416X-3.5147, R2=0.94. Based on the relationship, the number of adults per 10 plant which can cause 5% loss of yield was estimated to be approximately 10.1. And EILs was estimated to be approximately 1.0 adults/plant in late April.