Bloch type oscillations have been studied in a system of two small-capacitance and high-resistance Al-(Al)PbAu Josephson junctions connected in series and isolated from the electromagnetic environment by two high-ohmic metallic (Rs approximately=250 k Omega ) resistors placed very close to the junctions. The differential resistance dV/dI as a function of current I showed peaks at I=+or-2ef when the system was irradiated by microwaves at frequency f=400-800 MHz. The peak structure was pronounced in comparison with the one for a single junction in accordance with theoretical expectations from a larger charging energy. The effect can be explained within the semi-classical theory of Bloch-type oscillations.