Several morphological characteristics of each nymphal stage of Pseudococcus cryptus were compared. Antennae of slide-mounted individuals of each stage were observed under a differential interference microscope. The number of antenna segments of the first, second, and third instar, and adult females were 6, 6, 7 and 8, respectively. The length of the second and third antenna segments differentiated the first instar from the second instar nymph. Each instar stage was precisely discriminated by the number and length of antenna segments. To discriminate nymphal stages by external appearance, the body length, dorsal wax covering, and 17 paired marginal wax appendages were compared under a stereoscopic microscope. Nymphal stages could not be identified by body length alone. The first instar had only one pair of wax appendages, and the second instar could be distinguished from other stages by the appearance of 17 paired marginal wax appendages. The third instar could be differentiated from adult females by the combination of body length and dorsal waxy covering. The accuracies of the first, second, third instar nymph, and adult female, discriminated by combined observation of body length, dorsal wax covering and 17 paired marginal wax appendages, were 92.0%, 91.4%, 93.4% and 81.8%, respectively.