This study was conducted to evaluate of application methods including seeding furrow, foliar and drip-irrigation with imidacloprid in cucumber cultivation under structure. We investigated the uptake of imidacloprid and control effect on cotton aphid. Application of seeding furrow was treated with imidacloprid 20 mg a.i. per plant in planting hole at planting time, the maximum residue of imidacloprid was 17.4 mg/kg in upper leaf after 7 days treatment. Control effects on cotton aphid were maintained over 80% of control value until harvest initiation. Application of foliar with imidacloprid 5 mg a.i. per plant at harvesting season showed that the maximum residue was 8.78 mg/kg in upper leaf after one day and the residual fell sharply. The control value on cotton aphid was 47% after 7 days. Application of drip-irrigation was carried out at planting time and harvest season. At planting time in experimental plot with imidacloprid drip-irrigation 10 and 20 mg a.i. per plant, the maximum residual in upper leaf was 0.41 mg/kg after 12 days and 0.56 mg/kg after 14 days respectively, and the effect of control on cotton aphid was kept up over 80% of control until harvest initiation. At harvesting season, application of 5 mg a.i. per plant showed that the maximum residual in upper leaf was 0.62 mg/kg after 7 days. The control value on cotton aphid was 64% after 10 days. The maximum residue levels of imidacloprid in fruit were all below the Korean MRL, 0.5 mg/kg. As results, it could be suggested that application of drip-irrigation was effective for reducing the amount imidacloprid to control the cotton aphid.