Abstract: This paper reports the results from the observations on the stylet and the parasitic site segment of Japanese pine bast scale (Matsucoccus matsumurac Kuwana) on Masson's pine (Pinus massoniana).The results show that the stylet of the just hatched nymph coils as tendril on venter. When parasitizing, it stretches from the back of the inter-coxa of the anterior leg as a bundle composed of four equal needles, among which two needles embedded together. The average lengths of stylets for the initial parasitic and second instar nymphs are 1.209 mm and 1.625 mm respectively.It has been shown from the observation on parasitic site segment that its stylet can penetrate the phloem and injure the xylem of the pine tree. Then a small canal, which is 2.0-4.5 mm in length and 0.35-0.50 mm in width, will be formed in the xylem. But no tracheids can be found in the canal.On the same branch of the pine tree, the density of nymph population at the shady side is 3.71 times of that at the sunny side so that more injury will occur at the shady side of the branch.The results of observation on parasitic site segment of this pest show that the stylets stuck out from the nymphs penetrated phloem and injuried xylem of the pine trees, and induced a sheath shaped symptom in xylem. The length of sheath was 2.0-4.5 mm, and a width 0.35-0.50 mm. There were no tracheids visible in sheath.