To effectively use a multicore processor, processes should be distributed to each core. Furthermore, circumstances under which the distribution effect does or does not appear must be clarified. Operating systems (OSes) have two types of architectures: microkernel and monolithic kernel. A microkernel OS implements minimal OS functions as the kernel and most other OS functions as the processes, which are referred to as OS servers. A monolithic kernel OS implements all OS functions as the kernel. These two types of OSes have different distribution forms for processing. This paper evaluates the basic performance of the microkernel OS; further, it compares distributed processing between microkernel and monolithic kernel OSes. We employed AnT as the microkernel OS and Linux as the monolithic kernel OS. AnT is a microkernel OS developed for a multicore environment and Linux is a widely used monolithic kernel OS. Finally, this paper reports that microkernel OSes surpass monolithic kernel OSes in terms of performance of distributed processing in a multicore environment.