We were studying on the modeling of boiling water reactor fuel assemblies at pin-by-pin level by using Monte Carlo method. The designed boiling water reactor system is cylinder, and the radius of the cylinder is 228 cm. The total active core height is 315.79 cm. The reactor core was divided into the square lattice 7 x 7 type with a constant pitch of 30 cm. The core was surrounded with the reflector. The reflector was surrounded by SS316LN ferritic steel with width of 3 cm. The mixtures 0.21-% PuF4 and PuO2 were used as fuel. In this study, the effect on the neutronic calculations of PuF4 and PuO2 fuels was investigated in the designed boiling water reactor system. There were calculated k(eff), heat deposition and the fission energy in the designed boiling water reactor system. The three-dimensional (3D) modelling of the reactor core and fuel assembly into the designed boiling water reactor system was performed by using MCNPX-2.7.0 Monte Carlo method and the ENDF/B nuclear data library.