Abstract: This paper reports the tegumental surface changes of skin phase, lung phase and hepatic portal system (hps) phase of 8. japonicum schistosomula on ultrastructural level by using scanning electron microscope (SEM). The purpose of this study is to find the pattern of the tegument changes of this parasite in vivo, in order to compare with the material intended for immunologieal or prophylactic chemotherapeutic research work of schistosomiasis.According to our materials addition to the adult of S. japonicum, the paper published by He Ye-xum et al. (1980), it is comprehensive to make a comparison of tegumental changes from cercaria, three phases of sehistosomulae and to adult of S. japonicum, mainland strain.There are four points considered to be important:1. We revealed several annular troughs around the body of the cercaria (Fig. 1) and skin phase of schistosomula (Fig. 5). The same structure extends by having twenty or more in lung phase (Figs. 8, 10). While in hps phase the annular troughs are indistinquishable gradually due to the elongation and full grown of the body (Figs. 11, 14).2. The crests of schistosomula changes into complex form. There is a primitive pitted tegument in cercaria and a little modification on the surface of skin phase. The pitted tegument of lung phase begins to differentiat (Fig. 10). especially in the mid portion of the body. There is a dramatic change in hps phase by having honey comblike crests with differant layers on certain part of the tegument of 10-day schistosomula (Fig. 13). The crests of 15-day schistosomula become longitudinal rope-like structure, which connected up and down, left and right to form particular pattern in appearance (Figs. 16, 18). The same individual on certain area have a complicated deeply pitted tegument (Figs. 15, 17). Therefore the development of the crests is asynchronous.3. There is a little modification of spines in the skin phase schistosomule, but becomes less in number and disordered in the mid portion of the lung phase. "While the spines of anterior and posrterior parts of the worm remained unchange (Figs. 8, 10).4. The number of sensory papillae are so many in cercaria (Figs. 2, 3) and most of them were diminished in skin and lung hpase (Figs. 5—7). While in hps phase the sensory papillae become more abundant, particular on anterior and posterior part of the body and on two suckers. (Figs. 11, 15, 17, 21).We considered the changes of these 4 points above mentioned, really is an adaptation of migrating periods in semiquiescent metabolic state.While in hps phase the parasite starts a new growing period. Our observation showed the schistosmula of S. japonicum so much alike what Wilson et al. (1978) and Lawson et al. (1980) studied on S. mansoni sehistosomule.