We report on the temperature dependence of thermal conductivity of single crystalline and polycrystalline organometallic perovskite CH3NH3PbI3. The comparable absolute values and temperature dependence of the two samples' morphologies indicate the minor role of the grain boundaries on the heat transport. Theoretical modeling demonstrates the importance of the resonant scattering in both specimens. The interaction between phonon waves and rotational degrees of freedom of CH3NH3+ sublattice emerges as the dominant mechanism for attenuation of heat transport and for ultralow thermal conductivity of 0.5 W/(Km) at room temperature.