We have successfully demonstrated an 8-bit microprocessor using passive transmission lines based on single-flux-quantum LSI technology. In the microprocessor designed here, called CORE1α6, a simple bit-serial architecture with seven instructions was employed. In the CORE1α6, the floor plan was designed with consideration toward integration of a memory, and superconductive passive transmission lines (PTLs) were used to connect circuit blocks. Utilization of PTLs helped us reduce the propagation delay in long interconnections. The design flexibility of the floor plan was enhanced and the performance of the microprocessor was improved by 20% compared with our previous design. The CORE1α6 was composed of 6319 Josephson junctions and 15 PTLs with power consumption of 2.1 mW. We have confirmed the complete operations of the CORE1α6 by on-chip high-speed tests. The maximum clock frequencies for bit operation and instruction execution have been found to be 18 GHz and 1.2 GHz, respectively, where the performance corresponds to 240 million instructions per second (MIPS).