We present results obtained with a single photon counting system of 384 silicon microstrips (100 micron pitch) equipped with six RX64DTH ASICs including charge preamplifier, shaper, two discriminators and two 20-bit counters for each channel. The energy resolution of the system was determined to be of 0.72 keV (rms) with a spread of threshold setting of 0.32 keV for the whole 384-channel module (at energies of 29-33 keV), indicating its excellent potential for dual-energy imaging. Images of a mammographic test object made of PMMA, polyethylene and water were taken in scanning mode (strips parallel to incoming X-rays) under the dual energy X-ray beams. Images were subsequently processed with the dual energy subtraction technique (Alvarez and Macovski, 1976). Experimental results agree well with MCNP simulations of the mammographic phantom and demonstrate the capability of our system to obtain contrast cancellation between two kinds of materials, thereby enhancing the visibility of small features in the third material.