The present study was carried out in the field and laboratory to clarify the bionomics of an armored scale, Aonidiella taxus. The results are summarized as follows: 1. This armored scale is viviparous, nymphs being laid beneath the scales. Females have two nymphal stages and adult stage, whereas males two nymphal, prepupal, pupal and winged adult stages. The duration between settling of crawlers and nymph-depositing of adult females is more than 43 days at 25℃. Male adults emerge about 26 days after settling of crawlers at the same temperature condition. 2. Scale coverings of females and 1st instar males show almost circular form, while those of 2nd instar males are somewhat elongated. Therefore, the sexes can be easily discriminated after 2nd instar. The development of scale coverings is observed only at early few days of each instar. Size of scale covering of adult female is about 2.5 mm in diameter. 3. The thresholds of the development of male and female are 14.7 and 14.8 ℃, respectively. Thermal constant for female from settling to nymph-deposition is 447 day-degrees, and one for male from the same stage to adult emergence is 278 day-degrees. 4. The adults continue nymph-deposition for about 70 days. They deposit 2 to 6 crawlers per day. Mean fecundity of adults is 158. Net reproduction rate (R_0) is 59, the mean length of one generation (T) is 66 days, and the intrinsic rate of natural increase (r) is 0.04 per female per day at 25℃, respectively. 5. This species has 2 or 3 generations in Miyazaki and 2 in Fukuoka during a year.