A diffuser anti-rotation system and apparatus is described. A diffuser anti-rotation system includes a circumferential coupling ring interlocked between a top of a first diffuser and a bottom of an adjacent diffuser. One end of the first diffuser includes at least one male register tab, the opposing end of the adjacent diffuser has at least one female register slot, and the coupling ring interlocks with the male register tab and the female register slot. One of the male register tabs and one of the female register slots are aligned axially and a single projection from the coupling ring interlocks with both the male register tab and the axially aligned female register slot. Impellers are mated with and rotating within each of the first diffuser and the adjacent diffuser, and the interlocked coupling ring prevents rotation of the first diffuser with respect to the adjacent diffuser.