Abstract: Objective To evaluate the effect of inserting angle and direction of orthodontic force on stability of micro-implants in mandible and provide theoretical evidence for clinical selection of inserting angle and direction of orthodontic force. Methods Three-dimensional finite element models of mandible and micro-implants were fabricated. They were assembled using different inserting angles ranging from 30° to 90° (30°, 60°, 90°) and 4 directions of orthodontic force. Effects on the maximum von Mises stresses in mandible and micro-implants, as well as on the maximum displacements in micro-implants, were analyzed under the application of 2 N horizontal force. Results The distribution of stresses and displacements was lower with an inserting angle of 60°. The minimum stresses were 3.234 MPa (cortical bone) and 27.06 MPa (micro-implant) with an inserting angle of 60° when direction of orthodontic force was 45°. The direction of orthodontic force had no significant effect on cortical bone stress. Conclusion The inserting angle has statistically significant effect on stresses and displacements, as well as stability of micro-implants, and the recommended inserting angle is 60°. Direction of orthodontic force has less influence on the stability of micro-implants.