Experimental observation of the “Bloch oscillations” which are predicted theoretically in small Josephson junctions, resulting from their macroscopic quantum nature, has been made in superconducting granular tin films, the sheet resistance of which ranges from 3 to 12 kΩ at 4.2 K. We show that the values of 2ef obtained from the experimental V - I characteristics and a relationship I = 2ef are in agreement to within 0.3 % with those calculated using the frequency f of the microwave fields applied. It is one of the important conditions to observe the “Bloch oscillations” in the junction network that the number of parallel paths connecting two current electrodes is a few hundreds or less.