Objective　To study morphologic characteristics of S1 and S2 pedicles of sacrum co-existing lumbosacral transitional vertebra, and provide anatomic basis for sacroiliac screw fixation.　Methods　79 specimens were selected and measured in this study. Anatomic measurements included the anteroposterior diameter of S1, the height and transverse diameter of S1 and S2, the anterior and posterior heights of S1and S2 pedicles, the width of S1 and S2 pedicles, and the depth and the angle of screw in S1 and S2.　Results　For normal specimens, anterior heights of S1 and S2 pedicles were about (18.1±3.8)mm and (12.4±2.3)mm，the posterior heights (20.6±3.6)mm and (14.34±2.9)mm, the width (27.7±3.1)mm and (22.2±3.1)mm；For typeⅡ specimens, anterior heights of S1 and S2 pedicles were about (19.9±2.0)mm and (10.4±1.5)mm，the posterior heights (19.2±2.6)mm and (14.4±2.4)mm，the width (29.9±2.2)mm and (19.5±2.7)mm；For type Ⅲ specimens, anterior heights (18.5±3.0)mm and (9.5±2.0)mm，the postreior heights (16.9±3.1)mm and (14.0±3.0)mm，the width (27.8±2.2)mm and (18.6±3.4)mm respectively. The size of normal S1 pedicle was less than type Ⅱ，however, that of type Ⅲ was similar to the normal. The size of normal S2 pedicle exceeded that of type Ⅱ and type Ⅲ.　Conclusions　sacroiliac screws fixation is reliable for treating lumbosacral transitional vertebre. One or two screws can be hold in S1 pedicle, however, only one screw can be hold in S2 pedicle.