To improve the efficiency of biomass heating by microwaves, this paper studied numerically the heating of wood, sugar cane bagasse, orange peel and palm oil in microwave domestic oven. The study focused in the evaluation of power absorption capability of the biomasses in cylindrical and sphere shapes. The Maxwell equations were employed to calculate the microwave electromagnetic field distribution in the microwave cavity and in the samples, coupled to heat equation. Quantitatively, the power absorption capability and temperature distribution uniformity were, respectively, described by power absorption efficiency (PAE) (0.07 < PAE < 0.87) and the coefficient of variation (COV), varying between 0.01 and 0.14. Two dimensional plots of temperature evolution as function of time was used to determine the locations of the resonating peaks as function of peak number. The rate of heating efficiency was evaluated using the degree of thermal runaway ΔT (1K<ΔT<102K) and evolution of average temperature T¯ (298K<T¯<343K) and their relationship with the energy absorbed by the samples and COV, respectively. The comprehensive evaluation coefficient (CEC), that describes the usability of a specific sample in industry, varied between 1 and 14, was calculated for the biomasses and shapes.