The aim of this study was to quantify the effect of anti-pronatory and anti-supinatory foot orthoses on the angular displacement, velocity and accelerations of the rearfoot complex during gait. The transverse plane motion of the leg relative to the foot was used to indicate rearfoot complex pronation and supination. Three dimensional gait analysis on 12 subjects was used to derive the changes in the rearfoot kinematics due to the orthoses. The anti-pronatory orthoses decreased the range of pronation during the contact phase (p=0.0002) and the total range of rearfoot complex motion (p=0.000002), whereas anti-supinatory orthoses increased the range of pronation during the contact phase (p=0.00006) and the total range of rearfoot motion (p=0.049). Anti-pronatory orthoses also decreased the initial peak in pronation velocity during the contact phase of gait (p=0.006). Neither orthosis had a statistically significant effect on rearfoot complex acceleration.