The original approach to the creation of high-temperature single-electron tunneling systems has been developed based on the use of nanocluster molecules. The morphology and electron tunneling characteristics through single nanocluster molecules organized as highly-ordered monolayer Langmuir-Blodgett films on atomically-flat graphite substrate have been studied experimentally using scanning tunneling microscopy (STM) and spectroscopy techniques with sub-nanometer spatial resolution in a double barrier tunnel junction configuration "STM" tip - monomolecular film - conducting substrate" at ambient conditions. Molecular single-electron transistors on the basis of a single nanocluster molecule operating at room temperature were constructed and studied. Various nanocluster molecules with cores from 3 to 23 metal atoms were used as a central electrode in these transistors. Computer simulation of I-V curves of molecular single-electron tunneling (SET) transistor was carried out using the modified theory of single-electronics with consideration of discreteness of the energy spectrum of a molecule as well as the effects of energy relaxation of electrons in the molecule. A comparison of the simulated I-V curves with the experimental ones allow to conclude that the experimental data correspond to the slow energy relaxation case