In this paper, efficient parallel algorithms are proposed to find the majority element, with size n, in shared-memory and message-passing parallel systems. In a shared-memory system, the time complexity of our last proposed algorithmis is O(log n ) by using n/log n processors. Hence, it is cost optimal. Because these proposed algorithms do not require reading from or writing into the same memory location, they can be implemented on an exclusive-read, exclusive-write (EREW) model. In a message-passing system, we take into account the effect of communication time for three kinds of interconnection networks; cube connection array, linear array, and mesh array. Furthermore, even if the only comparisons allowed between elements are tests of equality, we can find a solution using our proposed algorithms.