Objective To quantify the morphometric characteristics of the pedicles of the infantile thoracolumbar spine and to determine the feasibility and safety of pedicle screw fixation in very young children. Methods A total of 52 patients younger than three years of age underwent standard spiral computed tomography (CT) were enrolled in this study. The patients were grouped according to age, group 1 (0 ～ 18months of age) and group 2 (18 ～ 36 months of age). Images were reformatted, and multiplanar reconstructions were used to attain images of thoracic and lumbar pedicles on sagittal, coronal and transverse planes.The measurements included the inner and outer pedicle diameters on the transverse plane, pedicle sagittal diameter, pedicle length and the pedicle angle on the transverse. Characteristics of the pedicles of the immature thoracic and lumbar spine were studied. Results Pedicle diameters on the transverse plane decreased gradually from T1 to T5 and increased gradually from T6 to L5. The shortest transverse diameter of the thoracic pedicle was T5 or T6. The inner diameter of the segment of L4 in infant (younger than eighteen months) was less than 3.0 mm and the external diameter less than 3.5 mm from T3 to T9. The inner diameter of the segment from T5 to T8 in infant (more than eighteen months) was less than 3.0 mm and the external diameter from T4 to T7 was less than 3.5 mm. The sagittal diameter was significantly more than the transverse diameter. Pedicle diameters on the transverse plane, the sagittal diameter, and the length of the pedicle changed significantly with age, but the pedicle angle did not changed significantly with age. Conclusions The pedicles in the segment from T3 to T9 of less than eighteen months and from T4 to T7 of more than eighteen months were too small, there was no feasibility and safety of pedicle screw fixation. So pedicle screw fixation was feasible and safe for below T9 segment in the infants who are younger than three years old.