Objective To investigate the characteristics of ultrasonogram of eyes with silicon oil tamponade. Methods Forty-seven patients (47 eyes) who had undergone the operation of silicon-oil removing were examined by A-(to determine the length of ocular axis) and B-scan before and after the operation respectively. The length of ocular axis and cubage of vitreous chamber were detected and the characteristics of the ultrasonograms were observed according to the default parameters of ultrasonograph. Results The results of A-scan showed that the preoperative axial length was 1.465 times of the postoperative one in the eyes without lens, and 1.284 times in eyes with lens; after modified the parameter according to the acoustic velocity, the preoperative axial length was (0.78±0.34) mm longer than the postoperative one in the eyes without lens, and (0.56±0.32) mm in eyes with lens. The results of A-scan showed that the cubage of vitreous chamber enlarged obviously in eyes with silicon oil tamponade, and the acoustic features included complete filling and partial filling according to the amount of silicon oil. Several arc echoes at the posterior segment of eye were detected in the silicon-oil-filling eyes with retinal detachment. Conclusion In the silicon-oil-filling eyes with lengthened ocular axis, the characteristics of B-scan images are affected by acoustic velocity through silicon oil, the amount of silicon oil capacity and the emulsification of silicon oil. (Chin J Ocul Fundus Dis，2004，20：349-351)