In the present research, wafer behavior during double-sided lapping was investigated. The wafer behavior was estimated based on double-sided lapping simulation, which was developed by authors. In the simulation, contact between the wafer, an upper plate, a lower plate and a carrier is considered, and the wafer behavior is calculated based on equilibria of the forces and the moments applied to the wafer. The behavior was estimated under several conditions, and the effects of lapping conditions to the wafer behavior was discussed. The variation of rotational speed of the wafer is larger in the condition where the rotational speed of the carrier is larger. The wafer rotates with the carrier without slip under the condition where COFs against the upper plate and the lower plate are different. And, the variation of the rotational speed of the wafer is smaller when COF against the carrier is smaller. Furthermore, lapping velocity, which is proportional to material removal rate, was calculated with the estimated wafer behavior, and it was confirmed that better flatness could be achieved under the condition where COF against the upper plate is same as COF against the lower plate and COF against the carrier is small.