The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is one of the major insect pests of cucumber, Cucumis sativus L. The spatial distribution and occurrence of Aphis gossypii Glover on greenhouse cucumber, Cucumis sativus L., were studied to provide an efficient and reliable sampling plan for its control. A highly clumped pattern was observed among plants (TPL b = 1.63) within a greenhouse. To develop a sampling plan for visual enumeration, leaves within plants were selected by different percentages of leaves (eg., 3rd and 6th, 6th and 9th leaf,…from the bottom of the plant) and then compared the accuracies and efficiencies by relative net precision (RNP). The results indicated that selecting leaves from the bottom of the plant by systemic sampling methods were relatively high as other sampling methods.