In this study, we proposed a thickness estimation method of tumor using a grasping forceps with sensors and evaluated the method by estimating the thickness of tumor models located in tissue models. Though palpation is an important technique for distinguishing a tumor, the palpation during thoracoscopic surgery is difficult because of the lack of tactile sense. In order to compensate the surgeon's tactile sense, we developed a forceps with two MEMS (Micro Electro Mechanical Systems) triaxial tactile sensors. By using this forceps, we proposed a tumor thickness estimation method focusing on the detected force difference according to the hardness of the grasping area. Then, we evaluated the thickness of tumor models located in the soft tissue models to prove the feasibility of our estimation method. The 5 mm and 10 mm diameter spherical tumor models located in the tissue models were estimated 3.3 mm and 10.7 mm, respectively. This result indicates the possibility that the proposed method enables to estimate the thickness of a tumor within an organ.