Liver cancer is one of the most common cancers in the world. There are different methods to cure it. Proton therapy is the best method, because the proton has short range and transfers maximum part of the beam energy to tissue in the Bragg Peak. Of course nuclear interactions of proton with tissue produce secondary particles like neutrons and they can increase the risk of secoandery cancer affections.The purpose of this research is calculation of proton and neutron absorbed dose in tumoral and healthy tissue of the liver in proton therapy. First proton source was considered as a disk to simplify the situation and located in front of the MIRD phantom. A spherical tumor of diameter 0.5 cm is designed and located in depths of 2.5,5 and 9 cm of the liver.Proton therapy with different source energies were simulated and optimized therapatic energies were assigned to be 86, 106 and 133 MeV for each tumor.Then proton, neutron and gamma absorbed doses in tumoral and healthy tissue of the liver were estimated by simulating the proton therapy with optimized energies. After that, passive proton beam delivery system with double scattering technology was designed and located in front of a soft tissue cylinder. Eight simulation were run so each simulation included a single step of range modulation wheel. Finally, the depth – dose curve was drawn for each step and SO were evaluated as proton-fluence-weighted sum of Bragg curves from the individual range modulation wheel steps. So, a uniform dose region of width 5 cm is formed in the total depth-dose curve. If the tumor is set in this region, it will absorb a high uniform dose. Then proton therapy of liver tumor was simulated. For this purpose a tumor of diameter 5 cm was designed and placed in depth of 11 cm in the liver. After that, the source was modeled as a Gaussian distribution function with a mean energy of 200 MeV. So, the appropriate range shifter was assigned and proton absorbed doses per sourse particle for tumor and healthy tissue of the liver were estimated to be 3.32×10 -12 and 4.57×10 -13 Gy/par.s . To invistigate the influence of secondary radiations, neutron absorbed doses per sourse particle for tumor and healthy tissue of the liver were also calculated as 3.37×10 -14 and 1.85×10 -14 Sv/par.s. In the next step, a tumor of diameter 5 cm in depth of 6 cm in the liver was designed and proton absorbed doses per sourse particle for tumor and healthy tissue of the liver were estimated as 1.94×10 -12 and 2.04×10 -13 Gy/par.s by simulation of proton therapy with mean energy of 180 MeV. Also the neutron absorbed doses were calculated as 1.61×10 -14 and 6.34×10 -15 Sv/par.s. The ratio of proton absorbed dose in tumor and healthy tissue of the liver was 9 for the tumor in depth of 6 cm and this ratio was 7.26 for the tumor in depth of 11 cm. The results showed that tumor absorbs the maximum dose while the healthy tissue absorbs the minimum dose. Since the neutron absorbed dose in healthy tissue increases the risk of secondary cancer affection, the consideration of methods to decrease the neutron absorbed dose is important.