: Proton therapy is nowadays one of the most effective and useful ways of treating various types of cancers . The most important feature of this treatment method is the delivery of the maximum dose to the tumor and cancer cells compared to other methods , while , low unwanted dose reaches the tissues around the target area .The purpose of this study is to calculate and estimate the dose rate proton, neutron and gamma in the tumor and healthy stomach tissue as well as in organs adjacent to the stomach with use the MCNPX 2.6.0 simulation code. The simulations carried out in this study were done in two stages: In the first stage, a water cylinder was simulated in plexiglas cover with elliptical cross section and with a height of 70 cm and a large diameter of 40 cm and a small diameter of 20 cm. Then, at each stage, a spherical tumor was simulated with water of various radius of 0.5 cm , 1cm ,1.5 cm , 2cm , 2.5 cm and 3cm at depth of 6 cm . A proton point source was considered at a distance of 7 cm from the center of the tumor, and then radiated with energies 50-350 MeV . In the second stage of the simulation, the mature adult male standard phantom was used to plan the treatment and determine the appropriate energy for the radia mentioned in order to higher precision and complete body simulation and considering the details of this phantom. At this stage, the actions taken were similar to the simulations carried out in the first phase with the difference that at this stage, this phantom was radiated from four directions: the anterior-posterior, posterior-anterior, right-lateral, and left-lateral . Among the four different geometries, the maximum proton dose was obtained in the anterior-posterior state. The maximum dose obtained in radia of 0.5 cm, 1cm, 1.5 cm, 2 cm, 2.5 cm and 3cm and in the anterior-posterior state were obtained at 85 MeV, 89 MeV, 93 MeV, 97 MeV, 101 MeV, 104 MeV. The results show that dose to the healthy tissue of the stomach in any radius relative to the maximal dose to the tumor has a much lower amount, which indicates the concentration and precision of the beam in the discharge of energy in the cancerous area.