A clearance model of inhaled man-made fibers (MMFs) was developed, and the calculated fiber numbers and dimensions were compared with the experimental ones using a glass fiber (GF), ceramic fiber (RF1) and two potassium octatitanate whiskers (PT1, TW). If the translocation rate by macrophages is constant and the effect of dissolution and disintegration can be ignored, the fiber number is expected to decrease exponentially with time. In the experimental study, however, the fiber number did not always decrease exponentially. In the case of RF1, the fiber number decreased almost exponentially and the diameter decreased linearly with the time. The clearance rate constant of GF during 3 to 6 months after the end of one-month exposure was greater than that during 1 to 3 months. On the contrary, the clearance rate constants of PT1 and TW during 1 to 6 months were greater than next six months. The diameter and the length of GF did not change significantly. The fiber length of PT1 tends to become longer with time although the diameter did not change significantly. Our theoretical model gives a satisfactory fit to these experimental results.