Abstract: Pure beta emitters have application in treatment of the patients with the malignant diseases. Imaging of pure beta emitters is possible trough bremsstrahlung imaging. If the presently available imaging devices are to be used the main problem will be setting of the energy windows and selection suitable collimator. In this study we determined the optimum energy window for bremsstrahlung imaging of P32 in liver imaging using Monte Carlo simulation. Gate Monte Carlo code was used to image the Zubal digital phantom. Activity was assumed uniformly distributed in the liver of phantom and attenuation properties of organs were defined using ICRU data. The pure spectrum of bremsstrahlung radiation from liver was simulated. The changes to this spectrum due to photoelectric and Compton interaction were determined. The useful range of bremsstrahlung radiation was determined and imaging was performed at 20 keV steps. The SNR and FWHM of the images were calculated and the optimum energy window was determined for LEGP and MEGP collimators. Analyses of energy spectrum showed the useful range of energy for bremsstrahlung images is 20-400 keV. Further analyses using the SNR and FWHM of acquired images showed that the optimum energy for both LEGP and MEGP collimators.