The cottony cushion scale, Icerya purchasi Maskell (Hemiptera: Margarodidae), is a destructive pest on citrus. This study was conducted to obtain the stage-specific phenology of I.purchasi for use in field application. The crawlers (hatched nymphs) from the egg sac of overwintered female began to move from late May and peaked in early to mid-June with most crawlers completed the movement till late June. The 1st nymph population peaked in mid June in 1stgeneration and early October in 2ndgeneration. The 2nd nymphs showed peak activity in late July and late October during the 1st and 2nd generation, respectively. The 3rd nymphs peaked in early September in 1st generation, while it kept a plateau without forming a peak after mid October in 2nd generation. The 1st generation adults peaked in mid September, and the tail was overlapped with 2nd generation adult population. Consequently, two life cycles were competed in Jeju area. An average of 20.7% of citrus orchards was infested with I. purchasi with a 3.9% of mean infested trees in Jeju. The present results should be useful in establishing management strategies for I. purchasi in citrus orchards.