Abstract: This paper presents the studies of the bionomics of the Yunnan pine bast scale, Matsucoccus yunnanensis Ferris (Homoptera: Coccidae). The results of the studies are summarized as follows:1. The scale insect causes a serious damage to Pinus yunnanensis Franch.2. The insect has two generations a year in the area of kunming, Yunnan. The two generations overlap each other. In the whole year around various stages of the insect, from eggs to adults, occur in the said area.3. It is found for the first time that the insect undergoes the parthenogenetic reproduction in both generations of its life time. Its allied species, Matsucoccus pini Green undergoes parthenogenetic reproduction in England only in the first generation but not in the second generation.4. The insect lays eggs intensively in the early and middle period. It could lay eggs continuously several days at day and night time. Most eggs are laid during 5—12 P. M. and 1—8 A. M. On average, 104—189 eggs are laid by a female.5. The degree of infestation of the insect is more serious in the pure forest than in the mixed forest.